CONDITIONAL 0

Use:       
The first conditional structure is used to talk about something which is always true. It always happens, on the condition that something else happens.
                Example: If it rains a lot, our garden floods.

Form:
1.            Make the first conditional in this way.

Examples:           If you fly on a budget airline, you have to buy your own drinks.  
                                When we visit Geoff, he always cooks us a roast dinner.

Or

Examples:           You have to buy your own drinks if you fly on a budget airline.  
                                Geoff always cooks us a roast dinner when we visit him.

2.            You can also form the zero conditional with the imperative form.
                                If you have a membership card, enter through the door on the left.
                                Enter through the door on the left if you have a membership card.

3.            You can also form the zero conditional using a modal verb.
                                If the alarm goes off, we should leave the building.
                                If it’s rainy and sunny at the same time, you can often see a rainbow.                                    
4.            Different tenses can be used in the If / When (‘condition’) clause. However, only the present simple, a modal or imperative form can be used in the ‘result’ clause.
                                If we’ve finished all our work, we can leave early.
                                If people are getting enough exercise, they usually feel better emotionally as well as physically.

EXERCISES:

https://www.examenglish.com/grammar/A2_zero_conditional.htm