Tutorial on stroke select in Designer and or Photo?

[Kuso77]

I'd like to select a continguous group of pixels (same color) and then stroke select them to draw an outline extending away from the selection. Rummaged through threads for almost an hour and couldnt find out how to do it, though I did see mention that stroke selection was possible in Designer.  Seems really complicated.  Could someone give me a step by step, or link me to a vid that explains the aforementioned procedure? 

I can do it gimp really easy, but I don't know how to do it in Affinity Designer or Photo.  I use Photo most of the time, but it seems I have to use Designer to do stroke selection.  Not sure though...

Thanks in advance for any help!

[R C-R]

Vector objects like shapes drawn with the Pen Tool have stroke & fill properties that can be edited (because they are defined geometrically). Raster objects like pixel layers are just a collection of pixels of various colors so they do not have stroke or fill properties you can create & select or edit as such. So to draw an outline or whatever on a pixel layer, you need to use a pixel based brush like the Paint Brush Tool.