pods come in on LR... if your pod poulation is very strong, sometimes you can see them on the glass when you first turn your lights on. They are very small, white critters, about the size of the tip of a ball point pen, maybe a little smaller.
If you don't have pods in your tank, or don't have a strong pod population, you can buy a kit that comes with, among other things, pods... but I'm drawing a blank on the name of the thing... it's pretty common, especially with people running refugiums... someone will let you know what it is.