http://www.englisch-hilfen.de/en/grammar/if_type1.htm

Use

It is theoretically possible to fulfil a condition which is given in the if-clause.

Form

if clause main clause
Simple Past would + infinitive
or
could + infinitive
or
might + infinitive

Examples

If I studied, I would pass the exams.
If I studied, I could pass the exams.
If I studied, I might pass the exams.

The if-clause can be at the beginning or at the end of the sentence.

If I studied, I would pass the exams.
I would pass the exams if I studied.