объясните каждую поставленную цифру,

 I (to see) John, I (to tell) him your news.
2. He (to be) very pleased if it (to be) really true. 3. If you (to go) to town
on Monday, you (to meet) my brother Tom. 4. If you (to need) help, my father
(to help) you. 5. We (to have) a picnic lunch if the day (to be) fine. 6. If
you (to ask) a policeman, he (to tell) you the way. 7. I (to finish) the job
tomorrow if I (to can). 8. I (not / to require) an umbrella if it( not / to
rain). 9. If she (to think) it over carefully, she (to form) a clear opinion.
10. If they (to catch) the bus now, they (to arrive) at half past nine. 11. He
(to find) the answers if he (to look) at the back of the book. 12. If you ( to
want) me to, I (to come) for a walk with you. 13. If he (to write) to her, she
(to answer) at once 

 He will be very pleased if it is really true.
 He would be very pleased if it was really true.
 He would have been very pleased if it had been really true.

If you go to town on Monday, you will meet my brother Tom.
If you went to town on Monday, you would meet my borhter Tom
If you had gone to town on Monday, you would have met my brother Tom.

 If you need help, my father will help you.
If you needed help, my father would help you.
If you had needed help, my father would have helped you.

If John doesn't oversleep, he won't be late for work.
If John didn't oversleep, he wouldn't be late for work.
If John hadn't overslept, he wouldn't have been late for work.

If he isn't late for work, his boss won't fire him. 
If he wasn't late for work, his boss wouldn't fire him.
If he hadn't been late for work, his boss wouldn't have fired him.