A Yes/No question is simply a multiple choice question that has yes & no as the only two choices. Yes/No questions are useful for asking binary questions. You can also construct a Yes/No question from a multiple choice question by specifying Yes & No as the only two choices in the question.
Using a yes/no question is as easy as dragging it from the left side of the page onto the right side of the page.
Watch this video tutorial on yes/no question types:
More on yes/no questions here.