when exactly do you use je voudrais and what about saying you would like, she/he would like, they would like-how do you say them?

You use the subjunctive "je voudrais", similar to its English counterpart, when you want to express a wish a bit more politely. Whenever you would say "I would like" instead of "I want" in English, consider je voudrais instead of je veux.

The conjugation across different persons:

je voudrais, tu voudrais, il/elle/on voudrait, nous voudrions, vous voudriez, ils voudraient.