Same Material / Texture / Shading / No. of Sides: Control which attributes a polygon must share with the current Active Polygon in order to be considered for selection.
3 Sides / > 3 Sides / 4 Sides / > 4 Sides: Control how many sides a polygon must have in order to be considered for selection.
Select: If pressed, all polygons that match the search criteria are selected, and all other polygons are deselected.
Add: If pressed, all polygons that match the search criteria are selected. Previously selected polygons are still selected.
Subtract: If pressed, all polygons that match the search criteria are deselected. Previously selected polygons that dont match the search criteria remain selected.