Will
Definition 1 of 4
Pro Tip 1/3
Time Specific
Use 'will' when timing is certain, especially with scheduled or planned future events. The train will depart at 6 PM.
Pro Tip 2/3
Instant Decisions
Use 'will' for decisions made at the moment of speaking rather than premeditated ones. It's hot here; I will open the window.
Pro Tip 3/3
Predictions
Use 'will' for predictions or expectations about the future, not past events. I think it will rain tomorrow.