UNIX & GNU/Linux - User commands - Using man

The man of Linux can help us to find some helpful information of functions.
This manual is splitted into eight parts.

1. General commands
2. System calls
3. C or other language library functions
4. Special files (usually devices, those found in /dev) and drivers
5. File formats and conventions
6. Games and screensavers
7. Miscellaneous
8. System administration commands and daemons

For example, to see the man of the open() function, you can use the:

$ man 2 open

or

$ man 3 open

The first will display the man of the Linux Programmer’s Manual.
The second will display the Perl Programmers Reference Guide.
If you want to see all listed mans, use the -k flag.
Example:

$ man -k *