Individually they are well described in the Help however, and reading this info carefully will give you a good idea of what each one does. The interactions and combined effects of these settings are complex to understand. Each one has a different method of mesh control and some of them can work together. There are seven numerical settings and three check boxes. In V4, the granular controls are presented directly the Density setting is not available as a slider. If you then push the Detailed Controls button in Windows Rhino, or the little down arrow in Mac Rhino, it reveals all the other granular controls that will allow you to completely control the process. Moving it to the left will result in fewer polygons and a coarser mesh, to the right in more polygons and a finer mesh. When you check Custom in Rhino V5 or V6, (Mac or Win) you are first presented with a simple slider controlling the Density setting. If you really want to control your meshing process, here is where you need to start!