Wayland = the GUI protocol. I'll try to build up the short version: Linux is modular, you don't have to have a GUI at all to run Linux. Most GUI systems themselves are modular, but a core component of the Linux GUI for a very long time has been a thing called X11. X11 is old and busted. Wayland is the new hotness. Some distros are using Wayland now. It offers some cool features that X11 either struggles with or can't do at all, but on the other hand there's lots of software that still doesn't work well with Wayland yet. I've been a Linux user for 10 years and the transition has been in the works the entire time.

Krita = a raster image editor/art app from KDE, the impression I get is that it's really made for digital drawing and painting, with some photo editing capabilities. GIMP (The GNU Image Manipulation Program) is more for "photoshopping." For vector art I would go with Inkscape.