SEVIS (Student and Exchange Visitor Information System) is an automated system that keeps track of students and exchange visitors and ensures that they maintain their status while in the United States.
In your first week in the US, tell your sponsor where you live (even if it is temporary) so he can register this information in the SEVIS database. Every time you move out, you must tell your sponsor to be in accord with immigration laws requirements.
Getting a social security number
SSN has nothing to do with health care plan. The SSN is the US equivalent of our French ID. You will need one to get paid, get a driver’s license, open an account, etc...
If you have a J-1 or F-1 VISA you can apply for a SSN at a Social Security Administration (http://www.ssa.gov/). To be eligible you must be in the Immigration Services file, which require to wait:
at least 10 days after you arrival on the US ground
at least 2 days after your SEVIS registration by your sponsor
Bring your passport and VISA papers (DS-2019, sponsor letter,…) to the SSA. You will receive your SSN in three weeks by mail.