Microverts are a group (just what we call them) of little living things in your tank. Most are arthropods, some echinoderms and mollusks and others. These arthropods are usually shrimp species. They are small, like the size of the ~ on your computer keyboard. They are great to have for many reasons. I won't explain, but for food, for removal of organics, for substrate agitation, and so on.
The easiest way to get them is to add a handful of live sand or live rock. You can always get a handful of sand from a club members tank, everyone has extra. They breed easily and will fill your tank unless: you have fish that eat them up, you have things like seastars eating them, you have filtration that removes them, or they lack a breeding area.
Try looking at your tank at night with a flashlight. You should see many little things running around on the rocks and on the glass.
Just my thoughts (certainly not an expert), hope it helps,
Adam