Depends on you want to transmit the data via CSD or GPRS.
For CSD, just dialup data call (make sure your SIM card has subscribed the data service) to the far end like typical line modem. When call is answered by the far end, handshaked, you can use the modem as a transparent data channel to send whatever data your want.
For GPRS, you need to dialup and make TCP/UDP socket to the server. Then you can send packet data through the channel. Check the WIP library for details.
One more question, when controller is ready to send data on UART1 of GSM module then how gsm module knows that that data is arrived on UART1.
onece data is arrived I have to make a data call. so which API I use to make a data call. In case I use fcm service.