Introducing the Linux file system tree
The Linux file system is like a tree turned upside down, as shown in the following figure. The top of the upside-down tree is represented by a /(slash) and is called the root. A series of limbs, branches, and leaves are below the root. The limbs are called mount points, the smaller branches are your directories and the leaves are your files. Each mount points is a disk partition, and the disk partition is mounted on the directory of the limb above it. When the disk partition is mounted on the directory branch, it turns that branch into another limb, allowing for even more branches to be positioned and attached below the mount point.
Normally, you need at least a root partition in your directory structure( the upside-down tree) and a swap space ( particularly if you have a system with under 16mb of RAM). Therefore, at a minimum, you should set up two types of disk space: a Linux file system starting at the root and a swap space. Theoretically; you don’t have to set up swap space, and some people choose not to. If you do, however you can run more programs than you have real memory you have on your system.
As mentioned, at a minimum, setting up a separation partition for your user files( usually called the home directory) is better and setting up multiple disks partitions for your Linux files is even better still. This setup makes backing up your files and updating your system to new versions of Linux much easier. The downside is that you have to leave empty space in each partition for new files, and these empty spaces add up. A reasonable analogy is using a filling cabinet to store your personal files versus a single box.