These are mainly earthworms and hard-bodied arthropods such as insects, millipedes, centipedes and arachnids. You don't need a microscope to see these animals...
Small soil invertebrates that are about 1-3 mm long. Springtails, mites, nematode worms and pseudoscorpions. You need a low powered stereo-microscope to see these animals properly.
These very small soil invertebrates are the single-celled animals, the Protozoa. You need a compound microscope to see these animals clearly.
These are soil fungi of which mushrooms and toadstools are the visible forms. And also the single-celled soil bacteria. You need a good compound microscope with high magnification to see bacteria and the single filaments of soil fungi.