Magic Wand tool
Now, what if you want to select an area that's all one color? You could spend time carefully outlining the area with the Lasso tool, but there is a much faster shortcut. You can use the Magic Wand tool.
Click on the Magic Wand icon in the toolbar. Your cursor will now look like a wand. The sparkly tip of the wand is the selection point. Click the wand on the image, and it will select an area of the same or similar color as the point that you touched.
Look at the Magic Wand menu. Just like the Marquee and Lasso tools, it also has addition, subtraction, and overlap modes. However, it has a new property: "Tolerance." The tolerance tells the computer how similar in color a neighboring pixel must be in order to be selected. A low tolerance means that the computer is very discriminating and the color must be almost exactly the same. A high tolerance means that the computer's judgment is looser and the color can be somewhat different. The pictures below illustrate clicking on the same point with different tolerance levels.
Note in the Magic Wand menu that the word "Contiguous" is checked. This means that the computer will only select contiguous areas of color. If you want to select all areas of the same color across the entire image, uncheck this box. The picture (below, right) shows the result of using the Magic Wand with the Contiguous box unchecked. (In this picture, the tolerance has been raised to 100.)