I just got my Raspberry Pi today model B revision 1.2. I got another PiFace Relay+ , PiFace Digital 2 and SainSmart 8ch Relay board. From here i don't know which board i should use to control multiple lights in my house. The RPi GPIO have 26pin while both PiFace have 40pin. Im worried that i may fried my RPi board. How can i control multiple light using the boards? Can someone point me to right direction?
I don't know where you got a model B, they were effectively superseded by the B+ more than 2 years ago, and are out of stock in most retailers. They are still a good system but are mainly used by people why have developed products for them.
You either need to get matching peripherals for the 26 pin GPIO or a newer Pi.
The 26 pins are largely compatible (there are a couple of changes, mainly to I²C) but they are mechanically incompatible with 40 pin peripherals. You may be able to use these with a 26 Pin cable.