'Am going to' is used for a plan or intention. 'Will' is used for a decision made at that moment. Here's an example. Two friends are choosing ice creams: A: What flavour are you going to have? B: I'm going to have vanilla. That's what I always have. A: That's so boring. Why don't you have something different. The blueberry one is amazing. I'm going to have that. B: Mmm, OK. I'll have that too.

Will- is the intention to do something in the distant future and "going to"- means that you plan to take action in the immediate future.

Hello Amna: Let's look at some sample sentences: I am going to buy the book. I will buy the book. I am going to succeed in this. I will succeed in this. I am going to be a leader in my field. I will be a leader in my field. I am going to pay the money now. I will pay the money now. I am going to raise this kitten. I will raise this kitten It IS going to rain. It will rain. This IS never going to end. This will never end. I am going to educate myself. I will educate myself. So basically, the different expressions are equivalent.