Connections for arduino uno,gsm sim900a,relay board,gas sensor

Hello,
I am a complete newbie to arduino. I intend to build an automation system that controls 3 bulbs via sms(on/off). Here i have attached the images of the components i have. Also i wish to use a gas sensor that sends an sms upon detection. I need to know the wiring schematics. Also i understand that the gsm module needs an external power source. How do i provide that?? Please do reply at the earliest.

Thanks,

gas sensor.jpg