if you fill the container they came in with water, the majority of the springtails will come to the surface. You can then either pour them into the terrarium, or, you can gentle blow on the surface (careful, they float easily into the air so aim to make sure they are going into the terrarium)
Pour out the extra water. Enough springtails will remain (unharmed) for you to keep the colony going in the original container. Add a few leaves, a pinch of brewers yeast. Occassionally add more yeast and a bit of slightly rotting vegetable (cucumber is good) and/or a piece of mushroom, or a bit of Baby rice cereal, or the occassion flake of fish food. And occassionally sprinkle a little of your supplement ontop too. Add more leaves once the originals are near gone.