Hi,
Let me know if a person gets his bacholar degree from US on F-1 status and he has not got any job offer in his specific field,can he still request for OPT.
Give me some details of OPT and its duration,if a person gets OPT how long he can stay in US and does he pay during his training

You can apply for OPT even you don't have a job offer. You need to apply for OPT 120 days prior to your completion.

First of all, OPT must be recommended by your school before submitting the application to USCIS. So you need to contact international office at your school and make an appointment for OPT.

You must bring the following documents to your OPT appointment

* the OPT Request Form, part II of which is to be signed by your dean, department chairperson or academic advisor.

* the completed I-765 form. (download from USCIS Home Page and make certain that the address you put in item #3 will be valid for the next 90 to 120 days as that is where your receipt and employment card will be sent). Mail from USCIS will not be forwarded by the US Postal Service

* A copy of your I-94 form (both sides) and a copy of the visa and identification pages from your passport

* Copies, front and back, of all previous I-20s

* Two recent photographs per the attached instructions from USCIS . Write your name and SEVIS number in pencil on the back of the photos. Do not cut to size or staple.

* A check for $340 payable to US Department of Homeland Security

After completion of studies, DO NOT leave the country without first receiving your EAD. Once you have graduated, you are required to show your EAD along with your other immigration documents in order to be permitted to reenter the United States. Printed on the EAD card will be the statement not valid for reentry.