So What is this SLI and crossfire stuff?

pretty new to the comp world, what is this stuff? I hear people talking about it in regards to video cards but thats all i was able to figure out... hah..

also what is pin? i see mobo's with like 240pin wtf is that

240-pin probably refers to DDR2/DDR3 RAM, as to distinguish it from older DDR RAM (184-pin). Pin counts refer directly to the physical number of connections that the RAM module has with the motherboard's DIMM slot. Its a small detail that you probably don't need to worry about. All you need to know is what type of RAM (DDR2, DDR3, etc.) your motherboard uses.