Since steel garage doors are so popular, garage door dents are becoming more and more pervasive. These gashes in the faade of your garage door (and therefore your home) are unsightly and may even pose something of a security risk. Sometimes, when the damage to a garage door seems superficial and simple to solve, you may be able to do it yourself at home.
Body shops used 'auto body filler' to repair cars that have been dented. This will fill in the dent, but require re-painting. Which can be fun, or a pain, depending on you.
An alternative is the 'suction cup' ding fix, which is another tool that is often used in auto body shops. You simply secure the suction cups to the door, and literally pull the impacted material back out.
These tools may not be directly available at a home depot or other home-improvement or tool store. You may need to get them online, or ask your local auto body shop. Acquiring the needed tools may be more expensive than the fix itself, so beware.
Of course, if you want to be one hundred percent sure that your garage will be competently fixed with no hassle, you may want to call in the professionals to do the job instead.