The tool bar in photoshop gives you lots of different options. I will go over the ones most frequently used. You can use your mouse to click on the tool that you want, however to increase your productivity it is beneficial to learn the shortcuts for each which I will indicate in parenthesis. Simply hit the letter on the keyboard and your tool will change. Also, many of the tools have mutliple options indicated by a small triangle in the bottom-right corner. If you hold down your mouse, you will see these other options.
Marquee (M) - This lets you select an area, which you can fill with color, move, delete, etc.
Move Tool (V) - This lets you move whatever layer is selected.
Lasso (L) - This lets you draw a selection. The polygon lasso tool will let you click your mouse at different spots until you complete the selection.
Magic Wand (W) - This lets you select whatever color you click on with your mouse.
Crop (C) - This lets you draw a box and then crop the image to whatever is included in the selection.
Eye Dropper (I) - This lets you select any color by clicking with mouse.
Brush (B) - This tool lets you select a shape and size from the options bar, and then use it as a brush. You can either click once to get a stamp effect, or hold down to get a brush effect.
Eraser (E) - The tools lets you erase! Choose shape and size from the options bar.
Paint Bucket(G) - This tool lets you fill in a selection with whatever color you have selected. It also has the option to fill with a gradient; this will use both the background and foreground color.
Text (T) - This tool will let you type. Drag your mouse to create a text area. Letter and Paragraph options are in the options bar.
Shape (U) - Use this tool to make a shape. Choose what shape you make in the options bar. If you hold down shift while you make your shape, it will have even proportions.
Hand (H) - This tool will let you drag your entire image around like you were holding it. Hold down the mouse to drag for a different view.
Zoom (Z) - This tool will let you zoom. Click to zoom in, hold alt and click to zoom out.