You need to have an output port for dvi or hdmi on your laptop, wire goes from that to your monitor and hey presto! You can also set your laptop to not shutdown or anything when you close the lid and then use an external kb and mouse as if it is a desktop computer.
Depends how much higher a resolution you'll be using on the monitor. If at all; I assume all new gaming laptops ship with a hi-res screen. I tried it with my old laptop and Diablo 3 struggled at 1080p on a monitor.