The zero conditional is used to make statements about the real world, and often refers to general truths, such as scientific facts. In these sentences, the time is now or always and the situation is real and possible.
The zero conditional is also often used to give instructions, using the imperative in the main clause.
If Bill phones, tell him to meet me at the cinema.
Ask Pete if you're not sure what to do.
If you want to come, call me before 5:00.
Meet me here if we get separated.
(Maria Fernanda Suarez)