In Zero Conditional or Zero Type Conditional, there is a real situation which always happens. It is close to First Type Conditional in meaning. Most exam questions ask the difference between them. However, it is easy to choose either. Zero Type Conditional expresses facts. We don't relate the conditions to past, present or future. They always happen.
Why do we use Zero Conditionals?
We use it to talk about scientific facts. The results are always true in relation to its condition.
If you don't feed your cat, it gets hungry.
When you turn this switch on, you start the engine.
How do we form Zero Conditionals?
We use the present simple in both clauses.
When you add more sugar, it gets sweeter.
If you don't add some starch or floor, your soup doesn't get thicker.