The Options Palette is very important in that it displays the available options for most of the tools in the Toolbox. The text tool has its own options and those are mentioned later in this documents. For everything else, all the options are shown here. The options for the Marquee tool are shown above. The shape can be changed from rectangular to elliptical, or a feather can be added to the edge of the selection.
Style can change from normal to a constrained aspect ratio or to a fixed width and height.
Each tool has its own options, so its good to experiment with each one as you need.