We use the conditional 1 to
speak to a real possibility in the
future; ie, an action that is likely
to occur in the future as long as
the condition is met.
structure
if + simple present + simple future.
It is used when a situation is real or possible.
examples
-If it rains today, I'll stay at home. -If she doesn't
call you, you can call her. -If you feel sick, you
must stay in bed.