When we want to talk about things that are always or generally true, we can use
If/When/Unless plus a present form PLUS present simple or imperative.
If you press this button, you get black coffee.
When you fly budget airline, you don't expect to get anything to eat.
Unless you need a lot of leg-room, don't pay the extra for first class.
Notice that we are talking about something which is generally true, not a specific event.
In the condition clause,
there can be a variety of present forms. In the result clause, there can
only be the present simple or imperative.
If you visit Barcelona, look out for the spectacular architecture.
If unemployment is rising, people tend to stay in their present jobs.
If you've finished everything, go home.
When you go to Barbados, take plenty of sun cream.
When I'm working, please be quiet.
When I've written a new article, I run it through my spell-checker.
Notice that 'unless' means the same as 'if not'.
Unless he asks you to continue, stop all work on the project.
Unless interest rates are rising, it's not a good investment.
- Unless you've been to Tokyo yourself, you don't really understand how fantastic it is.