To ask a question on Peter Answers, you simply type the question into the "question" box. However, in order to get an answer, you must type a period into the "petition" box and then proceed to write the answer yourself as the box fills up with a petition.
Peter does not actually answer your questions. It is simply a joke to play on friends. The idea is that "Peter " appears to answer seemingly impossible questions, when in reality, you type in the answers yourself in the "petition" section. Regardless of what question you ask in the "question" box, your answer will be whatever you typed in the petition.