Four Uses of Will
Will is used for things decided at the moment of speaking, and for predictions about the future that are more general (no specific evidence right now).
Decided right now, while speaking.
Committing to do something.
Volunteering to help.
Opinions about the future (no evidence).
Formula
Will vs Going To — the KEY difference
Imagine will as a lightning bolt ⚡ — it strikes instantly. If the decision was already in your head before you started speaking, use going to. If it struck you like lightning WHILE you were talking, use will. “I was already planning to go” → going to. “That just popped into my head” → will.