What does it mean "See something(3) or see something-else(5), etc..." in the man of a command in terminal?

Question

I have a simple question I made my self but didn't find any answer and hints.

When I type for the man entries of a command, e.g. "man git", I get the following:

...

DESCRIPTION
       ...

       See gittutorial(7) to get started, then see Everyday Git[1] ...
       The Git User's Manual[2] has a more in-depth
       introduction.

       After you mastered the basic concepts, you can come back to this page to learn what commands Git offers. You can learn more about individual Git
       commands with "git help command". gitcli(7) manual page gives you an overview of the command line command syntax.

       Formatted and hyperlinked version of the latest Git documentation can be viewed at http://git-htmldocs.googlecode.com/git/git.html.

Could someone explain what are those "See gittutorial(7)...Everyday Git[1]...gitcli(7)" etc.? I mean, I know that they are telling "look at this resource if you want to know the basic concepts, for more info, etc.", but actually how should one interpret it? What is the meaning of the numbers (like 7, 1, 2, etc..) inside the parenthesis or brackets? And where I can find the resources the manual is telling me to see, do I have to type something in the man prompt, or search on the Internet?

I just would like to ask for an elucidation.

Thank you for your attention!

Answer 1

Man pages are splitted into sections

to access a manual page inside a specific section you prepend the section number before the manpage name, for example try:

man 3 fork

or

man 2 fork

Usually the square braketed numbers are links to additional material in the NOTES section of the manpage (scroll to the bottom)

Answer 2

It means type man 7 gittutorial for more info. Man page are divided in numbered categories, sometimes overlapping. Use apropos git for instance to see the various possibilities.

Answer 3

The numbers in parentheses, manpage(N), are the manual section, each of the 8 sections covers a different topic.

See man-mages(7) ;) for a list of sections:

man man-pages

And you can open a manpage from a given section by including the number in the command:

man 7 man-pages

The numbers give you a hint of what the manpage will cover, e.g. time(1) is about a command, whereas time(2) is about a system call, and let you specify which section of the manual you're interested in when there's an entry with the same name on different sections.

The numbers between brackets, something[N] are footnotes, usually pointing to places where you can get more information.

Answer 4

The parenthesized numbers indicate in which section of the manual the referenced entry appears. Section (1) is commands (programs), section (2) is system call functions, section (3) is general library functions, etc. Some terms have distinct entries in multiple sections. For example, this ...

man 1 printf

... gives a different manual page (from section 1, describing the printf program) than does this ...

man 3 printf

... which gives a page from section 3, describing the printf() function from the C standard library.