[rewboss]

Unlike French, English has no true future tense. What is called the "will-future" is actually the present tense of the modal auxiliary "will".

There are a number of different ways of expressing things that will happen in the future:

Making predictions
We make predictions by using a modal verb followed by the infinitive: "It will rain tomorrow." The modal verb doesn't have to be "will"; "may" and "might" are also common: "We might have a white Christmas this year." We use different modal verbs to indicate how much chance we think our prediction has of coming true: "will" is near certainty, "may" is probably about 50%, "might" is less probable than "may".

Making promises and decisions
We make promises and decisions by using "will": "I will send you the money tomorrow" is an example of a promise. Or a decision: when the doorbell rings, somebody might say, "I'll get it!"

Talking about decisions that have already been made
Once a decision has been made, we use "going to" to explain what we plan to do: "I am going to watch that TV show tomorrow." Sometimes we literally mean "going to"; for example, somebody is putting on a coat and says, "I'm going to visit Sarah..." This is very similar to the French construction with "aller" plus infinitive.

Talking about things which are about to happen
We also use "going to" to describe something that is about to happen. For example, we might look up at the black clouds and say, "It's going to rain."

Talking about arrangements which have already been made
If we have already made arrangements to do something, we use the present progressive. For example, when you have booked your flight you can say, "I am flying next Wednesday at 10.30."

Talking about things that happen regularly
In rare cases, we can talk about something that we know will happen because it happens regularly; most often because it's timetabled. For this we use the present simple: "We're coming by train. It arrives tomorrow at 8.45."