Tu / Toi
In English you is used as subject and object personal pronoun but in French we use different words accordingly.
Tu is always subject:
Tu parles anglais. You speak English.
Où vas-tu ? Where are you going?
Comment vas-tu ? How are you?
Toi can be:
1/ Indirect object when the object is placed after the verb and after a préposition (avec, de, pour, sans, etc. when you want to say: for you, with you, without you, next to you etc.)
Je travaille pour toi I work/am working for you
Elle voyage avec toi She travels/is traveling with you
Je suis assise à côté de toi I am sitting next to you
2/ Subject in specific constructions when we want to emphasize on the subject:
Je vais bien, et toi? (I’m well, how about you?)
Moi, je suis française et toi, tu es belge. Me, I am French and you, you are Belgian