If you are inside your garage, you can manually open your attached garage door by locating the bypass switch. Simply look for the red rope hanging from the mechanism on the roof of your garage.
If you are outside the door, you may have a keyed emergency release bolted into the outside of the door. Simply insert the key and rotate 180 degrees. Then pull it out until you notice a popping sound.
For more information on opening your garage door, click here.