Going to is used to talk about the future when a decision or plan has already been made. It is not a tense but a structure using be + going + to-infinitive. Examples are "I am going to buy a new car" and "Are you going to paint the house?" Going to can also be used to make predictions about the future based on present evidence, such as "It's going to snow" based on a black sky or "You're going to miss your train" based on the current time.