Springtails (Collembola) are very small white hexapods (and no longer considered insects).
Springtails are very small, ranging from 1mm (0.03937 inch) to 6mm (0.23622 inch) and are therefore great food for very young newts that just lost their gills. As the newt grows springtails quickly become too small though, and will not be more than just a snack.
It's very easy to breed springtails. All you need is potting oil and some flower. Place the potting soil in an old aquarium and add a bit of flower. Make the flower wet with water. After a while the flower will start to rot and this will attract bacteria. These bacteria will be eaten by the springtails, thus they will grow and reproduce. That's all there is to it.
It might be difficult to catch springtails, because they're fast little creatures. As they live in potting soil there should be some solid clods of soil that you are able to pick up. These clods will have springtails on and inside them so placing one or more of these clods in your newt tank should provide your newts with plenty of sprintails.