Curricular Practical Training (CPT) is available to F-1 students who have been enrolled full-time (not necessarily in F-1 status) in a US university for one academic year prior to the start of CPT. You must be maintaining good status as an F-1 student and also be in good academic standing.
Bring these documents to ISFO (Williston Hall room 406) for review by an ISFO advisor. If all is in order, the advisor will authorize you for Curricular Practical Training by issuing you a new SEVIS I-20. The employer should have a copy of the I-20.
DO NOT EVER work before your CPT authorization begins or after it ends! It is the student's responsibility to track these dates and to refrain from working at other times. If you get another offer from the company or from a different one, you need to start the application process over again and request new authorization from ISFO.