Hey Gebreabzgi Pawlos,
GSM interfacing with microcontroller is very simple. First check what protocol supprted in your GSM module (i.e, RS232 , TTL , UART). If your module has TTL output then direct cross connect TX and RX pin of GSM to microcontroller's TX and RX pin and make the common ground. If your GSM has RS232 support then connect with controller through MAX232(TTL to RS232) converter.If you want to interface with PC then directly connect RS232 cable and open hyper terminal .If COM port of GSM found,you can test GSM module by AT command.
For more information refer following link: