I bought a subscription and it has movies on it. Each movie has a url "this movie is provided by xxxx". I went on that site and sure enough it was a movie streaming website.
Is there a way for me to do the same thing for and movie streaming site I want?
Definitely you can but you have to get the direct source from the site. The only problem with that is usually some CDN sites have daily token so links generated will be valid for a few hours or day depending on the source. Sometimes, they get take down also. PM me and I'll try to help you.
Yes, m3u's are just text files. Look at your m3u.
#EXTM3U
#EXTINF:-1,The Great Gatsby
http://MovieUrlhere.net/thegreat/gatsby
#EXTINF:-1, Die hard
http://MovieUrlhere.net/DieHard/BruceWillisIsGod
You can copy the format you see in your m3u and add your own movies.