Incremental saves are when a new save file is created; leaving the old one in the state it was in. This serves as a sort of extended undo if anything goes wrong. In the case of following a tutorial like this these incremental saves can provide a way back if the reader ever goes astray and doesn't realize it at first, as opposed to having to start all over, avoiding frustration.
Blender contains a powerful shortcut to make incremental saving easy. Carry out the following steps for incremental saving:
Select File | Save As… or press F2.
With the pointer over the file list press + on the number pad to add a number to the file name.
Click on Save As Blender File to create the new file.
The next time this set of actions are followed the number in the file name will be incremented by 1 automatically.
