Time clauses show WHEN something happens. Use WHEN, WHILE, AS SOON AS, UNTIL, BEFORE, AFTER. Important: In time clauses, use PRESENT tenses (not future) even when talking about the future!
Quick tip: Time clauses: WHEN/WHILE/AS SOON AS/UNTIL/BEFORE/AFTER. Use PRESENT tenses (not future) even for future time! I'll call when I arrive (not will arrive).
WHEN = At that moment
Use WHEN for a specific moment in time. When I arrived, when she called, when it happens.
I'll call you when I arrive. (present simple, not will arrive)
When she called, I was sleeping. (past moment)
When I see him, I'll tell him. (future moment, but use present)
WHILE = During that time
Use WHILE for actions happening at the same time. While I was working, while you're sleeping.
I'll wait while you finish. (during the time you finish)
While I was studying, she was cooking. (two actions at same time)
Don't call while I'm in a meeting. (during the meeting)
AS SOON AS = Immediately WHEN
Use AS SOON AS for something that happens immediately after. As soon as I finish, as soon as you arrive.
I'll leave as soon as I finish. (immediately when finished)
Call me as soon as you arrive. (immediately when you arrive)
As soon as I saw her, I knew. (immediately when I saw)
Common mistakes
Not "I'll call when I will arrive." — say "I'll call when I arrive.". In time clauses, use present tenses (not will) even for future. When I arrive (not will arrive)..
Not "As soon as you will finish, we'll go." — say "As soon as you finish, we'll go.". Time clauses use present tenses. As soon as you finish (not will finish)..
Practise it
Time clause? Use PRESENT tenses! When/while/as soon as/until/before/after + present simple or continuous (not will/would).