Magic Wand tool let you select a consistently colored area with a click without having to trace the edge of the object like lasso tool do.
Click on the tool palette or press W(or Shift+W again if Quick Selection tool is selected instead) to access Magic Wand tool.
Click on the area of image that you want to select. The pixel that you click determines the base color. The range of color that will be selected is depend on the amount of Tolerance you set, where default value is 32. The higher the Tolerance(maximum 255), the more variation of color will be accepted.
Note that you can quickly shift between Add and Subtract mode by holding Shift key for "Add to Selection" mode and Alt key for "Subtract from Selection" mode while using Quick Selection tool.
If checked the checkbox on the toolbar , it will create a selection based on all layers instead of just the currently selected layer.
If you turn on Contiguous , the Magic Wand tool selects only pixels that are adjacent to each other. If this option is turn off, Magic Wand tool will selects all pixels from entire image within the range of Tolerance.