Sometimes it can take a while for the sim to register.
What phone do you have joe? Try a battery pull out or resetting network settings and make sure you have 3g enabled on your phone. If you need any instructions on how to do these things, just ask or google it. :)
other things you could try
make sure flight mode/airplane mode does not have a green checkmark beside it
settings->more settings->mobile network
make sure network mode is set to GSM/HSPA/LTE auto mode
tap on network operators