These words are most helpful in questions.. But they are also used to say "the state of being." They are forms of the word "Be." Or 'to be.' So, the short sentence "I jump." lets us know you do that.. But now? When? Jump'ing' could help us know you are talking about now... But "I jumping" is not the way it is written or said. We want to hear that you are talking about 'your state of being.' So choose the 'Be' word that fits the situation. To know which fits takes a little studying. But after that, you will know "I am jumping" is the correct choice. And as SMRH pointed out, by moving the 'Be' word to the front, you will have a question which means, "is my state of being jumping?" "Am I jumping?"

We use does/do/are/is/am to make yes/no question. Do(plural)/does(singular) is for a present simple, is(singular)/am(only "I")/are(plural) is for present continuous. like "Do you like coffee? / Does he go there?" and "Is he singing that song?".. hope this help :)