SolarDude

Thank goodness a pro showed up. I got to learn something too!

In addition to the advice above, my attached video shows some basic techniques you can use to draw what I think you’re asking for. (I didn’t practice what I did in the video in order to show the sorts of things that can happen so you can see how I rectified some ‘issues’ I didn’t want.)
There are many others methods and functionalities you can use but the ‘best’ one(s) will very much depend on your precise requirements.
Try playing around with the techniques I’ve shown in the video to get yourself comfortable with the basics and then get back to us when you need more details on specific areas.
Note: To edit the text – where I have done so in the video – you need to double-click it once the text layer is selected.
2020-08-16_09-39-38.mp4

I am an absolute newbie in drawing digitally (though not drawing physically). I set myself what I thought would be a simple beginner, teach-myself project using Designer. Your tutorials seem to start with an  assumption of more basic knowledge (or jargon) than I have. I think my issue is a basic misunderstanding of  layers, or deciding or managing the sequence of actions. Sorry to feel so stupid, but I am missing the "logic" of the process. [Maybe what is needed is a video tutorial at this level of (mis)understanding and decision-making.]
 My project: I want to draw some simple rectangular shapes and add text within each that I can center vertically and horizontally in each rectangle. I would like a different fill color in each rectangle, and different stroke-width outlines to my rectangles. I would then like to connect my rectangles with lines of different stroke widths and/or colors. (Result, sort of like a simple mind-map.)
I'm fine with drawing, shaping corners, and filling the rectangles. Then I go astray. Adding text makes the rectangles disappear. Changing the color changes the color of the text. I cannot automatically align the text in the rectangles. I assume that my issues have to do with managing the layers in the layers panel, but maybe the text-alignment issues do not. Adding a text layer seems to make my "rectangle" layer disappear from the layers panel. I cannot seem to figure out what where it went. Should I add my text in the same layer as the original rectangle instead of its own layer? if so, how do I do this without making the fill and/or rectangle disappear? Art text? makes the text path curve around the shape of the rectangle, or something unexpected like that. (I still lose the color of the fill.) Text box? How do I fit it in the rectangle or not lose the fill color?  How do I use the opacity sliders for the layers? For example, setting the opacity to 0 in the text layer simply makes the text gray and disappear, not let that layer show the rectangle's color and shape behind it show through, etc. When, or why, do I add new layer?
Could someone kindly start me off with a very basic, step-by-step beginner's workflow to practice with to achieve my result? Or explain the logic behind sequencing the various processes to achieve my result? Such as: 
Step 1. select rectangle tool at left, draw and shape rectangle.
Step 2. color fill rectangle? or should I add text and align?
Step 3. set stroke around rectangle
Step 4. add new layer????  select text tool and type text???    etc., etc.
 

I've been at this stuff for a long time but only sporadically, so for all intents and purposes I'm a beginner.
I'll give you a method that will get you started and perhaps more knowledgeable users will jump in with a better idea.
AFAIK there's no way to format a text box to define fill, stroke etc. It's just a container for text. Off the top of my head the only way to achieve what you're after (formatted text on a formatted rectangle) is:
1. Draw and format your rectangle as before.
2. Select the text tool, click on the artboard and drag out a rectangle roughly the same size as the one you created.
3. Type your text in the text box, format as you like e.g. selecting center placement horizontally and vertically, size, text colour etc.
4. Notice that this operation has created a new text layer in your layers list tab in the "right studio" i.e. that tabbed section to the right of the screen.
5. With the move tool, select the text box and drag it so that it overlays your coloured rectangle.
6. Drag the edges of the text box so that it matches up with the rectangle beneath (or is centered therein or whatever relationship you'd like).
7. With the move tool, click and drag a selection that captures both boxes. That is, e.g. place the move tool outside the upper left corner of the rectangles, click and drag until it's past the lower right corner. You should now have both text box and rectangle selected. If you have the layers tab open you will see that both layers are selected.
8. You should see a "group" button on the tool bar, or you can go to the Layer menu and select "Group".
Henceforth the text box and underlying rectangle can be selected and moved as one.
If you double-click the object you'll be editing the text layer.
If you select the object, then select only the coloured rectangle layer in the layers tab, you'll be able to edit its parameters. There are probably also keyboard shortcuts enabling one to select the next layer down, dunno about this.
Worst case you can always select the grouped object and ungroup temporarily if you need to make a lot of changes to the underlying rectangle.
Also note you can grab the side handles and corner handles of the selected object and resize the frame/rectangle without altering the text size, or grab the extra handle off the lower right corner (there's an official name for this of course) and drag to resize and reshape the object in a manner that re-scales the content (text) at the same time. Pretty cool.
I'll see if I can attach a little, ugly example file here.
TextOverRectangle.afdesign

Alt, Ctrl and Shift is the Modifier key, which cannot be configured as classic keyboard Shortcuts (must be controlled directly by the application).

You don't need to switch to the Move Tool to move the Text Frame
Just move your mouse anywhere over the Text Frame bounding box (not the nodes) and the cursor will change to something like that shown below 
Then drag the Text Frame to where you want it - once done dragging you can "get back to editing text right where you were."

I came to the forum today looking for a way to replace a certain keyboard shortcut functionality I'm used to in Adobe products. Specific examples of operation given below are from InDesign; from what I recall Illustrator is pretty similar and Photoshop is a little different. I only found one post here that was even in the ballpark, so...
Scenario: you're editing text. Obviously you can't use "V" to select the Move tool; that will just insert a "v". OTOH selecting the Move tool with the cursor is a pain if you just want to do a quick move and get back to editing text right where you were.
The Adobe convention I miss: If you have the text tool selected (also applies to many other tools although not always in the exact same way) you can press and hold CTRL (PC) to switch the cursor to the Move tool only as long you continue to hold CTRL. As soon as you let it go, the cursor reverts to the Text tool (or whatever tool you were using).
But wait, there's more. Having pressed and held CTRL, you can then add SHIFT or SHIFT+ALT in order to zoom in or out, or if you add SHIFT+ALT and then release CTRL, you get the Hand tool and you can shift the artboard. When you release SHIFT+ALT, you're back to whatever tool you started out with. It's still second nature to me even after years of very infrequent use. Fast and hassle-free.
Correct me if I'm wrong but I don't see any way to add this kind of temporary tool select modification to the keyboard shortcuts myself.
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Disclaimer: I no longer use graphic design software on a daily or even monthly basis, and for all the years I've used Adobe products, I'd still call myself a noob. My copy of Adobe Creative Suite is v3, so... yeah. I should also point out that I am thrilled at the quality, facility and AFFORDABILITY of Affinity software. A boon for a guy like me who has a few skills that occasionally come in real handy, but rarely generate significant income -- certainly not enough to justify Adobe prices.