If you've already been issued a license and have upgraded at an exam session, soon as you get the signed CSCE, you will be allowed to use the frequencies allowed by your license immediately.
If you upgraded to general class (element 3), you will have to sign with "/AG" or "Temporary AG" or "Stroke AG" when you are on frequencies reserved for general and above. For example you would say, "This is KC1XXX temporary AG"
If you upgraded to extra class (element 4), you will have to sign with "/AE" or "Temporary AE" or "Stroke AE" when you are on frequencies reserved for extra class operators. For example you would say, "This is KC1XXX temporary AE"
Once the FCC ULS has updated with your new license class, you no longer have to add the temporary AG or AE suffix to your callsign. You also don't have to add the temporary AG or AE on frequencies that you were allowed to operate on with your previous license.
If you did not have a license and passed your element 2 along with element 3 and/or 4, you can not transmit until your callsign is issued in the FCC's ULS.  Once your license has been issued and appears in the FCC's ULS, you do not have to attach the temp suffix since you were issued either a general or extra class license.