When you say maybe, you're not completely sure about your answer. If you say you'll maybe study at the library tonight, it is possible that you'll go there.
Maybe is a shortened version of the Middle English phrase, "it may be." People use it when they're not sure about something — or they aren't ready to give their answer. Sometimes other things have to happen — or not happen — before you can be sure. For example, because it might rain tomorrow, you aren't sure there will be a baseball game. In the meantime, you answer, "Maybe," if someone asks if you are going to the game.
