Conditional If

Conditional tenses are used to speculate about what could happen, what might have happened, and what we wish would happen. In English, most sentences using the conditional contain the word if. these sentences are made up of an if clause and a main clause. 

Type 1

The type 1 conditional is used to refer to the present or future where the situation is real. The type 1 conditional refers to a possible condition and its probable result. In these sentences the if clause is in the simple present, and the main clause is in the simple future.

If clause	Main clause
If + simple present	simple Future
If this thing happens	that thing will happen
If you don't hurry	you will miss the train
If it rains today	you will get wet

Type 2

The type 2 conditional is used to refer to a time that is now or any time, and a situation that is unreal. These sentences are not based on fact. The type 2 conditional is used to refer to a hypothetical condition and its probable result. In type 2 conditional sentences, the if clause uses the simple past, and the main clause uses the present conditional.

If clause	Main clause
If + simple past	present conditional or present continuous conditional
If this thing happened	that thing would happen OR that thing would be happening.
If I spoke Italian	you would not be so tired
If it rained	you would get wet

Type 3

The type 3 conditional is used to refer to a time that is in the past, and a situation that is contrary to reality. The facts they are based on are the opposite of what is expressed. The type 3 conditional is used to refer to an unreal past condition and its probable past result. In type 3 conditional sentences, the if clause uses the past perfect, and the main clause uses the perfect conditional.

If clause	Main clause
If + past perfect	perfect conditional or perfect continuous conditional
If this thing had happened	that thing would have happened OR that thing would have been happening
If you had studied harder	you would have passed the exam
If it had rained	you would have gotten wet

Source : http://www.edufind.com/english-grammar/conditional/

Conclusion

Conditional tenses are used to speculate about what could happen, what might have happened, and what we wish would happen.

Type 1	is used to refer to the present or future where the situation is real
Type 2	conditional is used to refer to a time that is now or any time, and a situation that is unreal.
Type 3	3 conditional is used to refer to a time that is in the past, and a situation that is contrary to reality