You learn by choosing small projects and go bigger as your confidence increases.
buy a low priced shoulder (tooling leather) and don't be afraid to throw away first attempts
Ask questions at the tandy leather store like how do I use this tool, or "How would I do this...?" They are usually very helpful in hopes of selling tools.
Don't go crazy buying leather stamps, even tho they are relatively cheap, I find I used them starting out but rarely use them anymore (except for background texture).
If you are artistic at all and have basic hand skills - you will learn fast and be pretty happy with the outcome
Get the basic tools first:
A work surface
rawhide hammer (rubber bounces all over)
a selectable hole punch for buckles, snaps, rivets etc
rivet setter
swivel knife for designs (and tracing paper)
strap cutter,slicker and creaser for belts
a good utility knife with replaceable razor blades
You will use these tools over and over - buy quality as you can afford it.
This is mostly what I use, along with a few basic stamps for background texture
At some point a quality set of Shears is worth the investment too.
Have fun - make stuff you like for yourself first, if ye end up throwing a few away - at least there is no pressure from a paying customer...
mP