Your server’s filesystem can be thought of as a tree. The directory tree starts at the root, which is the lowest possible level in the directory tree. The branches of this "tree" are called directories. Directories can contain files and other directories.
The relationship between the root and any directory within the system is called a path. Paths are displayed with an initial slash (/) to denote the root, and subsequent directories are separated by additional slashes.
To move from directory to directory, you use the cd command. For example, to change into the /etc/mail directory, type the following at your command prompt:
> cd /etc/mail
You can verify your location within the filesystem tree with the pwd command:
> pwd
/etc/mail