I've never done it with cannabis, but I understand its the same way. With salvia, I take a razor blade, cut below a node at a 45 degree angle, pull off the leaves on the bottom node and put it in a glass of water. With salvia I keep them in a humidity chamber. Im not sure if marijuana needs this or not. Im sure a bit of research will pull up more details but I'll leave that up to you.
oops, almost forgot, it should sprout roots after a few weeks and then you put it in soil.
You can do it with distilled water, but cloning gel makes it a ton easier. and with Rootone at wal-mart being 4 bucks. why not make it easy. you also need a humidity dome as the only place it is going to get water is through the leaves until it roots. You can stick it rockwool, soil, vermiculite. as long as its a medium.
Hick's cloning guide has pictures and step by step instructions. Great How to. Thanks Hick. Use you imagination for a humdity dome.
note: It takes longer to root if the host plant was in the flowering stage. Less time if in veg.