If you have a substrate they will basically live off of that. With a dirt mix they can feed off of that, as well as decomposing leaves from your plants. Leaf litter is great for keeping springtails alive in tanks, gives them plenty of spaces to hide and establish themselves away from the frogs while still acting as a food source.
PS you should come check out frogday tommorrow in san jose since you aren't too far http://www.frogday.org
Like the other 2 guys said, just add them to a tank and they should produce. Leaf litter really helps them establish and hide from frogs as well. I was told of another method of using a small bin that would be sunken into the substrate that would be full of food for springtails (leaves, rotting vegatation, etc) where they would be heavily produced. It seems like a good idea, but not the prettiest looking thing... but not that hard to hide if you have leaf litter in your tank already. If I am not mistaken this idea was passed on to me by Eric M, correct me if I am wrong Eric.
Yes, I tried doing that method. I used one of those little condiment containers and poked some holes in the lid so the springtails could get out. Put some dirt in the bottom, some leaves and some pasta, I went back a few weeks later and there weren't any in there, so I guess it didn't really work. Maybe I'll try it again with different materials and an open top. But yes, it looks pretty lame to have a wad of plastic in naturalistic terrariums.
The way I understood it was that you had an open top on the contianer. I would want to hide the container myself, but I have had good success with my springtails with just leaf litter... so I will keep them that way for now.