once: conjunction

Once can be used as a conjunction, meaning ‘after’, ‘as soon as’. It often suggests that something is finished or completed, and is most often used with a perfect tense.

• Once you’ve passed your test I’ll let you drive my car.
• Once he had found somewhere to live he started looking for work.
• Once you know how to ride a bike you never forget it.

Note that we do not use that after once (not Once that you’ve passed your test …).

note

For present perfect instead of future perfect after conjunctions, (see here).