Future!

Simple Future has two different forms in English: "will" and "be going to." Although the two forms can sometimes be used interchangeably, they often express two very different meanings. These different meanings might seem too abstract at first, but with time and practice, the differences will become clear. Both "will" and "be going to" refer to a specific time in the future.

FORM Will

[will + verb]

Examples:

• You will help him later.
• Will you help him later?
• You will not help him later.

USE 1 "Will" to Express a Voluntary Action

"Will" often suggests that a speaker will do something voluntarily. A voluntary action is one the speaker offers to do for someone else. Often, we use "will" to respond to someone else's complaint or request for help. We also use "will" when we request that someone help us or volunteer to do something for us. Similarly, we use "will not" or "won't" when we refuse to voluntarily do something.

Examples:

• I will send you the information when I get it.
• I will translate the email, so Mr. Smith can read it.
• Will you help me move this heavy table?
• Will you make dinner?
• I will not do your homework for you.
• I won't do all the housework myself!
• A: I'm really hungry.
  B: I'll make some sandwiches.
• A: I'm so tired. I'm about to fall asleep.
  B: I'll get you some coffee.
• A: The phone is ringing.
  B: I'll get it.

USE 2 "Will" to Express a Promise

"Will" is usually used in promises.

Examples:

• I will call you when I arrive.
• If I am elected President of the United States, I will make sure everyone has access to inexpensive health insurance.
• I promise I will not tell him about the surprise party.
• Don't worry, I'll be careful.
• I won't tell anyone your secret.

No Future in Time Clauses

Like all future forms, the Simple Future cannot be used in clauses beginning with time expressions such as: when, while, before, after, by the time, as soon as, if, unless, etc. Instead of Simple Future, Simple Present is used.

Examples:

• When you will arrive tonight, we will go out for dinner. Not Correct
• When you arrive tonight, we will go out for dinner. Correct

There are some more here and here.