It’s not the long words in English that are confusing, it’s the short ones:
Jack: What kind of stuff are you into?
Jill: I’m really into kickboxing.
(If you’re into it, it means you enjoy it as a kind of hobby.)
Jack: Are you still upset about me breaking your mug?
Jill: No, I’m over it.
(If you’re over it, it means you have stopped being upset about it. Sometimes we say, ‘gotten over it’)
Jack: Fred told me he didn’t know what an MP3 was!
Jill: He’s not really with it, is he?
(If you’re not with it, it means you are not very clever or up-to-date. This phrase is most often used in the negative.)
Jack: Can I borrow your iPad?
Jill: Sure. I’m done with it for today.
(If you’re done with it, it means you are finished with it. We sometimes say, ‘through with it’ as an alternative.)