Zero & First Conditional

In zero conditional sentences, the tense in both parts of the sentence is the simple present.

if + present simple, ... + present simple

If this happen that thing happen

Example:

Ask Pete if you're not sure what to do

The first conditional has the present simple after 'if', then the future simple in the other clause:

if + present simple, ... will + infinitive

Example:

If it rains, I won't go to the park.

The first conditional describes a particular situation, whereas the zero conditional describes what happens in general.