The word можно has many other uses as well. For example, you could point to a door and ask if you can enter by asking можно? or you could point at a seat and ask if it’s free by using the same word.
Let’s learn another word of high similarity and importance:
Russian for necessary is нужно.
Both possible and necessary are just approximations and not exact translations for these words. As for нужно, it is used in the sense of it is necessary or it is needed. For example, you could say is it necessary to go? (нужно идти?), is it necessary to give documents (to you)? нужно дать документы?) and so on.