Present and present continuous to denote future?

OK, so if the present continuous is supposed to denote an action that is happening RIGHT NOW, why to we also use it to denote the FUTURE, as in "What are you doing this weekend?" or "I am having a barbeque on Friday". Also, it seems we also use the present simple to denote future time, as in "I have a meeting tommorrow at 9:00 am". So, how in the world should a student understand when to use the present, present continuous or for that matter future (will or be going to) to denote the future? I sure don't know how to explain it!

Typically, "will" is used for decisions made on the spot, while present and present cont. are used for plans already made ("be going to" is nearly the same as present cont., as far as I know).

Present and present cont. require a time to be stated or implied by the context, otherwise they are not future.

A good teaching order is:

1. present, which they probably already know ("I have a date")
2. present with a stated future time ("Tomorrow I have a date")
3. will future ("I will do that tomorrow, honey" - promises)
4. present cont. with stated furture time ("What, now? I am doing that tomorrow" - plans)
5. "be going to" ("I am going to do that tomorrow" vs. "I was going to do that tomorrow")

That's all I know, maybe someone else knows more.

Good Luck.

OK, that's pretty good. But there are many cases where you can only use one option. For example, why is it only OK to say "tomorrow I have a date" and not "tomorrow I am having a date" (both are plans already made). As a native speaker, the only one that sounds right to me is the first one, but is there any way a non-native speaker can decide this?

I forgot to say that you would also say "I have nothing to do tomorrow", wouldn't you? meaning I haven't arranged anything yet.

Hi~I am a junior in Taiwan.
I think it's right that the present continuous is supposed to denote an action that is happening RIGHT NOW. However, "will" is equal to the phrase " be going to".
For example,
I will do my homework tomorrow. = I am going to do my homework tomorrow.

I give you some examples about the present simple and presenht continuous.
1.They are showing a film calleed Bandit County. --- to show an activity in progress now.
2.The trouble with this place is it's becoming too crowded. --- to show a changing state.
3.What time does the film start? --- to show a scheduled event.
4.Look, she's getting out of that black limousine. --- to show a temporary activity around the time of seaking.
5.TV personalities and film stars often stay there. --- to show a regular or habitual activity.
6.It costs about $10 for adults. --- to show a permanent state.