The yes/no questions are formed from indicative sentences by using particle Ĉu at the beginning of the sentence:
Ĉu vi havas domon? – Do you have a house?
The question-word question are created by using an interrogative correlative:
Kion vi faras? – What do you do?
Kiu estas tiu? – Who is that?
Kiam vi alvenas? – When do you arrive?