By default the left button is used for selecting and the right button generally shows a menu of options for ther particular application.
By launching the Mouse icon in Control Panel you can change the default settings for your mouse. Most importantly you can reverse the left and right mouse buttons...
If you've got a three-button or scroll mouse, your list of options becomes vast indeed. Logitech MouseWare includes a "Webwheel" function for web navigation as well.