First Conditional

We are talking about the future. We are thinking about a particular condition or situation in the future, and the result of this condition. There is a real possibility that this condition will happen. For example, it is morning. You are at home. You plan to play tennis this afternoon. But there are some clouds in the sky. Imagine that it rains. What will you do?

IF	condition	result
	present simple	WILL + base verb
If	it snows	I will stay at shovel the sidewalk.

Notice that we are thinking about condition that will happen in the future. It is not snowing  yet. But the sky is overcast and you think that it could snow. We use the present simple tense to talk about the possible future condition. We use WILL + base verb to talk about the possible future result. The important thing about the first conditional is that there is a real possibility that the condition will happen. Here are some more examples (do you remember the two basic structures: [IF condition result] and [result IF condition]?):

IF	condition	result
	present simple	WILL + base verb
If	I see Tom	I will tell him.
If	Lynne is free tomorrow	she will invite her.
If	they do not pass their  driver’s ed test	their teacher will be disappointed.
If	it snows tomorrow	will you shovel the sidewalk?
If	it snows tomorrow	what will you do?

result	IF	condition
WILL + base verb		present simple
I will tell Tom	if	I see him.
He will invite Lynne	if	she is free tomorrow.
Their teacher will be disappoined	if	they do not pass their driver’s ed exam.
Will you shovel the sidewalk	if	it snows tomorrow?
What will you do	if	it snows tomorrow?

Sometimes, we use shall, can, or may instead of will, for example: If you are good today, you can watch TV tonight.

Source:  EnglishClub.com