Hi Katherine. You should see an indicator on your phone's display that you're using data. Also, in some phones you can disable data usage. Let me know which phone you have so I can give you more information about it.
To deactivate data connection press and hold the power button until a menu appears. Scroll down and choose Data network mode. This should deactivate data connection. If you want to use data again you just need to do the same steps again.