The conjunction if, even if, when, whenever, whether and unless often appear in conditional sentences.
If (Simple Present Tense) →Main (Simple Future)
1. If I win the lottery, I will go to Singapore.
2. If you finish your homework I will give you a ice-cream.
3. If he works hard he will rank first in the class.
If (Past tense) → Main (Would) + 1st Form of verb
1. If I had a pencil, I would give it to you.
2. If I knew her number, I would call her up
3. If you supervised it, the whole operation would be very easy.
If (Were) → Main (Would) + 1st form of verb
1. If I were Prime Minister, I would do a great job.
2. If I were going to London, I would bring your book.
If (Past Perfect) → Main (Would have) + 3rd Form of verb
1. If I had won the lottery, I would have gone to London.
2. Had she not known about if she would have stayed longer
3. If we had found it earlier we would have presented it to them.