Nmap is released under a GPL-style license, the full text of which is available in the COPYING file.
The latest version of this software as well as binary installers for Windows, macOS, and Linux (RPM) are available from https://nmap.org/
Full documentation is also available on the Nmap.org website.
Questions and suggestions may be sent to the Nmap-dev mailing list.
Ideally, you should be able to just type:
./configure
make
make install
For far more in-depth compilation, installation, and removal notes, read the Nmap Install Guide on Nmap.org.
Nmap has a lot of features, but getting started is as easy as running nmap scanme.nmap.org. Running nmap without any parameters will give a helpful
list of the most common options, which are discussed in depth in the man
page. Users who prefer a graphical interface
can use the included Zenmap front-end.
Information about filing bug reports and contributing to the Nmap project can be found in the HACKING and CONTRIBUTING.md files.