When you start Photoshop, the Tools palette appears at the left of the screen. Some tools in the Tools palette have options that appear in the context-sensitive options bar. These include the tools that let you use type, select, paint, draw, sample, edit, move, annotate, and view images. Other tools allow you to change foreground/background colors, go to Adobe Online, and work in different modes.
You can expand some tools to show hidden tools beneath them. A small triangle at the lower right of the tool icon signals the presence of hidden tools. Get a short description that documents every tool Photoshop's Tool Palette has to offer. A great reference guide for Photoshop users.