• 'Will' is an auxiliary verb. So, the verbs that follow 'will' must be in the infinitive.
• 'Will' is used to:

(a) Talk about a prediction.

(b) Express willingness or to talk about an action you want to take immediately after you have mentioned it. 

• Examples:

(a) She will meet Mr.Adam next week. 

(b) I think it will rain later.

(c) I will help you. 

• The verb after 'be + going to' should also be an infinitive.
• 'Be + going to' is often used to:

(a) Talk about plans or decisions that have already been made. 

(b) Predict something in the future, based on the evidence we can see.

• Examples:

(a) I'm going to be a doctor when I grow up. 

(b) Look at those dark clouds. It is going to rain soon. 

• For 'Wh-' questions, the subject or pronoun should come after 'will' or the 'be' verb. 
• For questions that require 'Yes' or 'No' answers, start the sentence with 'will' or the 'be' verb.
• Examples: 

• It is used to:

(a) Show a future action that is not planned or intended, such as a normal event.

(b) Show an action that will be happening at or by some future time. 

• Examples:

(a) They will be working till midnight.

(b) He will be returning by the time lunch was served.