Nmap is released under a custom license, which is based on (but not compatible with) GPLv2. The Nmap license allows free usage by end users, and we also offer a commercial license for companies that wish to redistribute Nmap technology with their products. See Nmap Copyright and Licensing for full details.
The latest version of this software as well as binary installers for Windows, macOS, and Linux (RPM) are available from 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.