You will recall that the first partition was for the operating system. The entire directory structure branches off a single foreslash ("/"). This is called "root" for short. Therefore, Partition 1 is abbreviated "/", meaning everything that starts with a "/" (unless, of course, it is declared otherwise in this window).
Partition 2 was for the user "home" directories. The directory which holds the user files is called appropriately "home." Because this (like every other directory in Ubuntu) branches off the root directory, we reference it with "/home".
Finally, Partition 3 is for virtual RAM, or swap. So select "swap" under "Mount Point" and ensure that "Partition" begins "Partition 3..."
The new partitions will be automatically set for reformatting. However, if you have pre-existing partitions, you need to decide whether you want to reformat them.
Reformatting destroys all the data on the disk. If you have a Windows partition that you are trying to preserve, you want to ensure that the "Reformat" box is NOT ticked.
Similarly, if you have pre-existing partitions which you would like to assign to a given place in the file system, here is the place to do it.
When you are done, the window should look something like this.