Click 'Buffer' button to do buffer; dbl-click an existing point feature to create buffer polygon;
Click 'Simplify': button to do simplify; dbl-click an existing feature to simplify; hold Ctrl key and draw a feature on map, when finished feature will be simplified;
Click 'Project' to project a feature to EPSG:900913: dbl-click an existing feature to project to EPSG:900913; (see results in Firebug console)
Click 'AreasAndLengths' or 'Lengths' to calculate lengths and areas of a feature; dbl-click an existing feature to calculate lengths and areas;(see results in Firebug console)
Click 'LabelPoints' to label point in polygon; dbl-click an existing polygon feature to label points;
For 'MultiPolygon LabelPoints' to label point in multiple polygons, first select muliple polygons on map and click 'MultiPolygon LabelPoints' to label points;
For 'Relation' first select any two existing features on map and click button 'Relation' to calculate if they are in INTERSECT relation; (see results in Firebug console)
Click "Clean up" to clean up identify results.