If you would like to practice using NMAP commands, the nmap organization has made available a test site at scanme.nmap.org. You can use this as your target when learning how to use nmap.
Here I’m running a scan against the website scanme.nmap.org and piping it to a file. The results of the scan are shown below.
Just don’t run continuous scans against the site, after all, it is a shared resource.