When you are learning English, it may seem that the language has little interest in the present, but is obsessed with the past and future. This may well be so. Celebrating or regretting the past, or planning for the future, do seem to take up a lot of energy and time in English. The multiple possibilities for talking about the future certainly seem to suggest we do it a lot. And it can be a bit confusing.
However, it is becoming simpler. If you look in an old-style grammar book, you will find a complex set of “rules” for when to use Future Simple (“will”), when to use “going to,” when to use Present Progressive for future, and when you can use Simple Present for future. In particular, a lot of effort was put into (in some cases, is still put into) the difference between “will” and “going to.”
Except that, at least in spoken American English, it really almost never matters. Plans? “I’m going to visit Europe someday” is more common, but you can say “I will” in the same sentence, and nobody will care. Predictions? “I think it’s going to rain tomorrow.” “Oh, really? Well, I don’t think it will rain for at least a week!” In fact, the only clear difference between the two now is that “will” is still the only way to talk about a sudden decision. “We are going to lunch now.” “Wait, I’ll come with you.” “I’m going to come with you” means a plan, and you can’t have a sudden plan.
Okay, what about the other two? In cases of a plan (but not a prediction), you can use Present Progressive for future if you say it is the future. Therefore, at noon, if you say “I’m leaving,” you mean now, but if you say “I’m leaving at 5,” you clearly mean the future. And Simple Present works only for predictable events (like scheduled trains and planes), or human behavior that is so often repeated that it seems like a schedule. Thus, “The train leaves at 6” works, as does “The boss goes home at 5 every day.”
I’ll admit, this is not as easy as -ed on a regular verb makes it past, but there’s not too much to deal with here. Some readers of this blog will disagree with me, and some grammar teachers will start screaming, but I suggest just making the whole future thing as simple as you can in your mind. Nobody is going to get upset about it.