General Reporting Requirements for Standard Post-Completion OPT:

The regulations require a student on post-completion OPT to report "any change of name or address, or interruption of such employment for the duration of the authorized training," and for the DSO "to reflect these reported changes for the duration of the time that training is authorized."  

The SEVP Portal Account:

You will receive an email from the SEVP after your OPT is approved and the employment dates are "active", meaning the start date of the employment is current.

You will be required to report new employment, changs in employment and cessation of employment. 
Please see the study in the states information page at https://studyinthestates.dhs.gov/sevp-portal-help for a wealth of information on the SEVP Portal

If you  do not receive an email from the SEVP by the start date of your OPT employment, send an email to isss@temple.edu.