Sorry, I don't have time to make a tutorial. But it's really quite easy...
The colours that wrap around the edges of the cube shape are just simple gradients (straight not rounded). You can set that exact colour and configuration with the gradient tool.
You just create one of the rounded slabs duplicate it twice, place it above and re-colour each as needed.
The arrows are made with strokes (or lines) making sure the edges of the strokes are rounded. The hexagonal shape is made up of lines (or strokes as well as the arrows.
The first rounded slab will have been made in the regular affinity view along with the arrows and hex lines. Then they will have been transferred to an isometric view (or plane) using Affinity's nifty fit to isometric view feature. There are a few other approaches you could take. Like making the slab in the iso view and just making the corners rounded.
However, I can appreciate that you're a noob so some of the concepts I'm talking about might seem confusing, but honestly they are pretty easy, (when you know how).
Youtube will provide you with everything you need here. I just did a quick search, there might be better ones tbh. But have a look at these: