We use Going to ; for something which is planned before ! And Will , for something that we decide to do at the time of speaking (suddenly may be) , or a probability in the future ! Example : 1- Tomorrow i'm going to the beach . (i'm sure that i'm going to go , i planned everything) 2- Tomorrow i will go to the beach. (i just decided it at the moment , maybe i will go maybe no)

Yes. Look at some examples PLANS 1) One day I will get married. That's my general plan but perhaps I don't even have a girlfriend yet. 2) We're going to get married. That's closer to reality. I've got a girlfriend and I'm thinking about it PREDICTIONS 1) I hope he will come. (I have no idea what will happen) 2) I;m going to be late. (There's a big traffic jam)