Actually, (be going to) usually comes after (will) in a sentence. For example, it is not right to say "She (be going to) France." Instead, you say "She (will) (be going to) France." To break it down, (be going to), specifically (going to) expresses an action. (ie: She is (going to) France-- the word (going) says what 'she' is doing. (Will), on the other hand, is usually NOT used to express an action. It usually comes before the action in the case of expressing something someone has yet to do. However, "She will go to France", "She is going to France"., and "She will be going to France" all have the same meaning.

Confused yet? The fortunate thing is that even if you misuse "will" or "going to" you will still be understood. You are going to get a lot of different opinions but in modern English the two are pretty much interchangeable when used in the future tense except in the following cases: Use only "going to" when you have a plan or intention. I am going to the beach next Wednesday. (plan) I've already decided. I am going to buy a new car. (intention) Use "will" when you are expressing your will or willingness. We need some more milk. I'll go to the store and get some.(willingness to go) I will definitely be there on Friday! (expression of your will) Don't know how to use a computer? Don't worry I'll help you. (willingness to help) There are cases where it is not clear which you should use. In that case people will understand your meaning. "Going to" and "will" are frequently misused even by native speakers ...so don't worry!

In fect.simpllify to say,"be going tol"used in a sentance which is you already have planned to do ,but "will"is u decide to do it in a moment time or in some emerge situations.

When we want to talk about future facts or things we believe to be true about the future, we use 'will'. * The President will serve for four years. If we are not so certain about the future, we use 'will' with expressions such as 'probably', 'possibly', 'I think', 'I hope' * I hope that you will visit me one day. If you are making a future prediction based on evidence in the present situation, use 'going to'. * The traffic is terrible. We are going to miss our flight. At the moment of making a decision, use 'will'. Once you have made the decision, talk about it using 'going to'. * I will call Jenny to let her know. Sarah, I need Jenny's number. I am going to call her about the meeting.