Recovery mode

http://www.macissues.com/2014/03/21/how-to-access-recovery-mode-in-os-x/

How to access Recovery Mode in OS X

OS

OS

DVD installation

OS

Insert your recovery DVD and reboot the system

Hold the C key when your system sounds the boot chimes

OS

Local Recovery

OSOSOS

Reboot your Mac

Hold the ⌘+R keys down when you hear the boot chimes

OS

The recovery drive contains a number of tools for reinstalling OS X, setting firmware passwords, and resetting system account passwords (click for larger view).
Internet Recovery

Mac Book Pro (13-inch, Early 2011)

MacBook Pro (15-inch, Early 2011)

MacBook Pro (17-inch, Early 2011)

iMac (21.5-inch, Mid 2011)

iMac (27-inch, Mid 2011)

MacBook (13-inch, Mid 2010)

MacBook Pro (13-inch, Mid 2010)

Mac mini (Mid 2010)

MacBook Pro (15-inch and 17-inch, Mid 2010)

iMac (21.5-inch and 27-inch, Mid 2010)

MacBook Air (11-inch and 13-inch, Late 2010)