Question

In fact I wanna know if I just say what I have, you'll understand me! For exemple: there's coffee and milk, what do you prefer?

Answer 1

Yes, you can say, "There's coffee and milk; which do you prefer?"

Or, you can say, "Do you want coffee or milk?" "Do you prefer coffee or milk?" is more formal.

Another formal way would be, "Would you like coffee or milk?"

You don't have to say "either/or."