A conditional sentence is a complex sentence with a subordinate clause of condition that usually begins with the conjunction IF. The clause of condition (the if-clause) indicates the conditions under which the action in the main clause may be realized.
Conditional sentences are usually divided into three main types:
1. zero conditional (such sentences say what is usually true or always happens under certain conditions)
If+present in subording clouse, present in principal clause
If it rains ,I drive to work(I always do this when it rains)
2. first conditional(Such sentences say what will or may happen in the future under certain conditions.May is less certain than will.)
If+present in suboding clouse, Future with will or may inprincipal clouse
He won't go to work ifhe fills ill.
3. second conditional (such sentences say what might happen in the future under certain conditions or how things might be different under unreal conditions in the present
If + Past or were in the suboding clouse, would/might +Inf in principal clouse
If you asked him,he might lend you some money.
If i were you,I would follow this piece of advice.