Games : How do I use the /particle command in Vanilla Minecraft?

The command instructions say "/particle < name > < x > < y > < z > < xd > < yd > < zd > < speed > [count] [mode]", but how do I use those? I understand the x, y and z, but first of all, what are xd, yd, and zd. Also, what does the speed do, and how much does any given number change it? What do count and mode do? I basically just want to know what everything in < these > or [these] do for the /particle command, and how I can effectively use them. Thanks.