Quick Selection tool can be use to quickly "paint" a selection using an adjustable round brush. As you paint the area you want to select, the selection expands and automatically finds the edges of the object you want to select.
Click 
on the tool palette or press W to access Quick Selection tool.
Adjust your brush size with [ and ] key. Paint inside the object you want to select as shown in the example on the right.
By default, the Quick Selection are in "Add to Selection" mode. The mode can be change from the toolbar 
, you can change the mode to "Subtract from selection" by selecting the icon on the right with minus(-) sign, it allow you to paint the area that you want to remove from your selection.
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.
Auto-Enchance 
reduces the roughness of the selection boundary. It automatically apply edge refinement. Note that you can also manually apply enchancement with the 
dialog.