We use (past simple; present simple; future simple) to talk about:
Something that is true in the (past; present; future).
Examples: i live in London.
The Earth is round.
You`re twenty.

Something that happens (right now; regulalry) or all the time in the (past; present; future).
Examples: I go to school 6 days a week.
Tom and Jim play football every Saturday.
My mum usually bakes a cake for my birthday.

Something that is (sometimes; always; never) true according to the scientific facts, habits, unchanging situations or general truths.
Example: Mars is the Red planet.
The human body contains 206 bones.
Bears sleep in winter.