To ask questions, just add か (ka) at the end of the sentence.

Paul ですか？(Is it Paul?)

We can also use words interrogatives to make more complex questions.

Dare (Who)

だれ です か? (Who is it?)

Doko (Where)

どこいぬですか? (Where is the dog?)

Nani (What / What)

Nan if before a word starting with t-d-n otherwise nani

なん です か? (what is it?)

あなたはなにがひつようですか (What do you need?)

Itsu (When)

いつ しゅっぱつ します か (When are we leaving?)

Generally speaking, question words replace information we don't know in the sentence.

いちごのくるまどこですか? (Where is Ichigo's car?)

The answer could be

いちご の くるま はがっこう にあります (Ichigo's car is at school.)