Grammar: 1st Conditional / Conditional 1

The first conditional is used to express situations based on fact in the present or future (things which may happen).
Uses the simple present tense:-

Formation

(IF Clause)	(Main Clause)
If I see you tomorrow,	I will buy you a drink.

or...

(Main Clause)	(IF Clause)
I will buy you a drink	if I see you tomorrow.

We often use unless which means 'if ... not'.

Formation

(IF Clause)	(Main Clause)
Unless you hand in your homework,	I won't mark it.
means
If you don't hand in your homework,	I won't mark it.

or...

(Main Clause)	(IF Clause)
I won't mark your homework	unless you hand it in.
means
I won't mark your homework	if you don't hand it in.

Note! We never use will, or won't in the if clause.
For example:

• If I have time today, I will phone my friend. = I will phone my friend, if I have time today. (It is possible that I will have time - therefore the condition is real).
• If I go to England, I will buy some Cheddar cheese. = I will buy some Cheddar cheese, if I go to England. (It is possible that I will go to England - therefore the condition is real).