tempdb growth and shrinking tempdb
Tempdb is recreated whenever the instance is restarted.  At startup tempdb is created at the size specified in the system catalog.  This means if you define tempdb to be 10GB, and it grows over time to 100GB, then you restart the server, tempdb will now be 10GB again.

The question about shrinking is one loaded with bad connotations.  For a discussion around that, refer to this question.