Format of filename is pretty arbitrary. The maximium length is 256 characters. No restiction on format is imposed, such as the 8 characters followed by a dot and a 3-character file extension. File extension is not essential, but using file extension for most commonly used file types, such as GIF, JPEG, HTML, etc are recommended. Using .exe for binary executable is absolutely not necessary (see files in /bin).
No drive, i.e., no "A:", "C:", "D:", and so on.
Everything starts with root "/" (different from the root user account).
In DOS/Windows, you refer to a file as a combination of drive and path, e.g.
C: 
TEMP HOMEWORK.TXT. In Linux (or Unix),
it is simply a path to the file, e.g. /home/yuni/my_homework.txt. It is
still true even if you have more than one harddisk, because the concept of
"drive" is made hidden by filesystem. In Linux (Unix), the distinction of
filesystem and hardware drive is very clear. The advantage is obvious. When
new disk is added and some files from the old disk are moved to the new disk,
no programs or scripts need to be changed to honor the new disk.
Common directories in Linux are:
Figure 2: Example of a basic Linux filesystem