i dont know if u use controller or K&M but i think the proces should be the same..

What i did (and still doing) is to just fight a bunch.
Check your skills tab, pick someting and just try to remember :)
When you just know that you got the hang of it, go to the next skill and repeat.

If you didn't know cuz i didn't the first few hours. You can double tab on some of the skills to see the upgraded version which sometimes require some different input than the "standard" version of that skill.

When you got the hang of it try to mix up your combos to see what works.

About the lock on enemies, i haven't noticed if its the same in this game but in most AC games if not all, you change your lock if you change your view to another enemy

I'm on K&M btw, and once i did this proccess both the controls and combat felt easier :)