I had a question about visa status and employment.

1>I have gone from F1 to OPT to F1 and by end of July I will be done with the program.
2>How do I get to work in the US since I have used the OPT?
3>Will I have to leave the US?
4>If the answer to 3 is 'Yes' is there anything that can be done about it?
5>If my employer file my H1B can I start working immediately?
6>After my program is done, do I have any grace period to get my things in order?

Are there any pointer you can give me which would make it easier for me to start work after my program is done with in August?