Click System Preferences from the Apple Menu at the top left corner of your screen.
Click to select Startup Disk from the System Preferences window.
Click to select the system you want to use to start up your computer. If you have just installed Boot Camp you will likely want to choose Mac OS X on Macintosh HD or similar.
NOTE*: You can also use this menu to start up from a network drive or restart the computer in Target Disk Mode.
Once you have select the system you would like to start up with click the Restart... button.
When asked to confirm the restart click the Restart button.
Your computer will then reboot using the system you selected!