The best thing you can do against Jhin is letting him use his crit on a minion than go in for a quick harass and let your support follow up for an all-in. don't all-in before level 6 though. jhins level 6 isn't really a powerspike for him since he can't use it mid fight, unlike your ult wich is a big powerspike.

If you're up against caitlyn you should just give up. wait for ganks and for engages from your support. dont harass since caitlyn easily outpokes you. you'll be fine if you play safe.

Jinx is a very hard matchup for vayne because she has alot of outpoke/outdamage potential. stay safe, wait for ganks and you'll be fine.

The first combo is: Q aa, aa, E. this will do damage to your opponent and knock them away so they can't return any damage. make sure to not use it often because it will drain your mana.

R, Q, E. this will make you go invisble so the enemy can't position themselves up for your E. make sure not to forget using your E for the extra stun.

R, Q, Flash, this will make you go invisble and turn in front of them, great for an E in your team. just like a lee sin kick flash.

E, Flash. this will reposition your E. recommend looking it up on youtube than practising it in the practise tool.

Good luck!!