The easiest way to store your personal files and configuration is to have a "/home" partition during installation. You can think /home as "My Documents" under Windows. Now you will need to install your Ubuntu on the "/" partition. You can think of "/" as "C:" under Windows. You will need at least 2GB for the "/" partition. However, if you plan to install some programs, Ubuntu recommends you to get at least 8GB for the "/" partition. Also make sure you have a swap partition which is the same or double the size of your RAM.
In summary, you can have the following configuration for your disk partition:
/ --> 16GB or more
/home --> the rest goes to here
swap --> 2GB