You simply invert the normal sentence structure (an affirmative sentence such as "Du stannar på en kopp te" which would translate as "You are staying for a cup of tea") so that instead of Subject-Verb- Object, it's Verb-Subject-Object. Hence: Stannar (verb) du (subject) på en kopp te?
Han går hem = He walks (is walking) home. Går han hem? = Is he walking home?
Du känner honom = You know him. Känner du honom? = Do you know him?
If I've made any mistakes, anyone, then please correct me! :)