Send AT command using GSM library

I'm using the GSM library from GitHub - MarcoMartines/GSM-GPRS-GPS-Shield: GSM/GPRS & GPS Shield Library for modules using SIM900/SIM908 with a sim900 shield.

I would like to send an AT command to the module using this library. There are a number of things in the list of what the library can do which look like they might do the job but I'm not sure which one to use. Here's the list GSM-GPRS-GPS-Shield/List.txt at GSMSHIELD · MarcoMartines/GSM-GPRS-GPS-Shield · GitHub