If you have the Dock always displayed, but there are times when you want it to go away, there are several ways you can achieve this. They all are different ways to turn on Dock hiding, which hides the Dock until you mouse over it.

1) Go to System Preferences > Dock, and check the box next to "Automatically hide and show the Dock". If you are just doing this as a temporary change to accommodate a program that takes up a lot of space, this is the slowest way to do this.

2) On the Dock itself, right click on the separator between the applications and the other stuff (don't know what they call the section with the minimized applications). Select the "Turn Hiding On" option and the Dock will go away. To fix it back, do the same thing but then select "Turn Hiding Off". This way isn't the quickest, but it doesn't require you to remember much of anything special.

3) Hit Command + Option + D on your keyboard. This shortcut is not obvious, but if you need to show/hide the Dock a lot this is the quickest way to do it.