Bought a sim card from 7-11, now what? S3

[netrate]

I have a s3 that I purchased from Kijiji. I want to use it with a SIM card, bought one at 7-11 ($10 micro), installed it and turned the phone on. It says the SIM card is inactive. What is the next step?

 

[B. Diddy]

When you buy a SIM card at a convenience store, it has to be activated (either by the store clerk or by the carrier). Which carrier is the card associated with? Were there any instructions on the packaging?