Your professor may limit the number of Internet sources you can use. Generally, when they say "web site" or "online source" they are not referring to articles you find in the online Library databases.

"Do you like HBO© or Showtime© ? You know how you can get a few channels with an antenna for free, but you pay more money to get the premium movie channels like HBO© or Showtime©, right?"

The Library's research databases are sort of like these premium TV channels because the Library pays money ($1,000,000+ per year!) to get the "premium" scholarly information versus the free information you can get on the Internet.

Providing libraries with these databases is a billion dollar business; database companies want to continue getting this revenue so scholarly articles are not "free" on the Internet.