Photoshop, illustrator, gimp, they all have that vector/pen tool.
Dunno about krita and all this new stuff though, but they should have it.

Its how I, and most other people got started here.

Ive known a few people who got quite good at using the mouse to draw manually though, its all about refining, draw rough, then zoom and refine, zoom and refine etc.
Once you get used to the PC specific stuff like layers and the tools and functions you have available, things get easier.

Its all about learning: practise lots, draw lots, fail lots.
Compare your sketches to others, figure the mapping out and how the sphere works etc.
The same principles apply from the real world.