If you are interested in learning more about nmap please take a look at https://nmap.org/nmap_doc.html. Also, for all those who would rather use a graphical interface to nmap, there is zenmap. Why don't you open it and try a few scans with it? Lastly, if you want to try a target on the internet for some testing of nmap or zenmap, try it against scanme.nmap.org. This site is available as a training aid for you to do scanning as long as you don't get too aggressive with your testing.