Texturing the base is a way of saying that you are adding material on the base to represent where the mini is residing. Could be a field, rocky area, or marsh/swamp.
Many materials can be used to accomplish this. I use Elmers Wood putty and have very good results. You probably should do this before painting the mini, that way the material doesn't get on the freshly painted feet and legs. Get the putty pushed down and around the base and feet. You can add rocks or trees, grass to get the look you are trying for. Hope this helps. O0