In addition to learning Blender's native boolean operations, I highly recommend you check out a free Addon called BoolTool (version 0.2)
Here is the link to the addon.
Here are my notes for using the BoolTool addon.
It makes booleans so easy that you can use Blender like ShadowBox in ZBrush.
Q. How do I use the BoolTool Add-On?
A. Create a cube. Duplicate the cube (Shift+D). Drag the duplicated cube (Brush object) so that it intersects with the original cube (Canvas object). Shift+RMB click to add the original cube (Canvas object) to the duplicate cube's (Brush object's) selection. In the BoolTool Tab in the ToolShelf, under Brush, click either Union, Intersection or Difference (or click on each one to see what they do). You will now see the Brush object perform according to the selected operation under the Brush Menu. Making a Brush object works great as a mask to cut in or add detail. The Canvas properties will affect the Canvas object. With the Canvas object selected you can also use the Brush properties which will obviously affect the Brush object. You can modify the Brush object in the 3D View such as scaling it or duplicating it to make multiple brushes. By selecting the Canvas object you can also manipulate a selected brush object in the Brush properties such as hiding it, applying it or removing it.
If you don't want to make a Brush, you can simply select what would ordinarily be the Brush object and then add the Canvas object to the selection and then just press the operation under Direct and a boolean operation will be performed. The results of the boolean operation will be stored in the active selection (the last selected object) and you can have multiple objects that act as Brush objects.
Here are the hotkeys as found in the Object menu:
Brush Union = Ctrl+Numpad Plus
Brush Difference = Ctrl+Numpad Minus
Brush Intersection = Ctrl+Numpad Asterix
Direct Union = Ctrl+Shift+Numpad Plus
Direct Difference = Ctrl+Shift+Numpad Minus
Direct Intersection = Ctrl+Shift+Numpad Asterix
Note: BoolTool will automatically convert Curve objects to mesh objects when you apply it as a Brush or Direct Boolean operation.
To use the Draw Poly Brush, switch to the view that you want to work such as Front view and then click on Draw Poly Brush. You will have a grease pencil that you can use to draw lines. Simply click where you want each point to be. You don't need to close the poly. The two open endpoints will automatically be closed. When finished drawing, press Enter and the polygon will be created. Poly Brush size will scale the depth of the polygon. You can use the Poly Brush as a Brush or Directly.
Inside the BoolTool AddOns Preferences, you can check Fast Transformations (marked experimental and disabled by default).
Fast Transformations replaces the G/R/S hotkeys for a new custom version that handles Boolean operations faster. The Blender viewport can struggle with high poly models when trying to carve out parts of the canvas. With this enabled, there will be a new option in the Brush properties that says Fast Vis, which when used, will allow the visibility to be changed on the fly. Use it if your workflow is being bogged down. Note: with Fast Vis on, it will be enabled for all the brushes.