The simple present tense is used in the if clause, and the tense in the main clause is the simple future tense.

EXAMPLE: If you leave now, you'll arrive home early.

We can turn the two clauses the other way round so that their positions are reversed as follow:

Whether the if-clause or the main clause comes earlier, both conditional sentences as above are acceptable.

• With the first conditional, we use the present tense to talk about the future. We use this conditional when the situation in the if-clause appears likely and there is a possibility of it happening.

EXAMPLE: If you help me with this, I'll buy you a drink. (You might help me)
EXAMPLE: If I see him tomorrow, I'll tell him the good news. (I might see him tomorrow)

• The first conditional refers to the present condition that is real and a probable outcome.

EXAMPLE: If the weather remains fine, we will go to the beach.
EXAMPLE: If you continue to feel better, you will be out of the hospital soon.

• Going to can be used in the first conditional to refer to a future event.

EXAMPLE: If she finishes work early, we are going to a restaurant for dinner.
EXAMPLE: If you don't hurry, we are going to miss the train.