Apache, which is the most widely used web server, has login facilities built in - if your site is relatively low traffic this words fine. You just need to create a file with user names and encrypted passwords using freely available more or less standard encryption software. If you are expecting upwards of hundreds of users this quickly becomes unmanageable and you'll want a back end database.
However, this is all probably academic since you'll almost certainly be using some pre-written forum/gallery/guestbook/whatever software, which will already handle the user management. There's probably free open source software available for whatever you have in mind. See what existing software package out there is closest to what you think you want to do, and the login part will almost certainly be included.
Do you need/want your site to be interactive and have input from your users, or will you simply be posting videos and articles for consumption? This is one of the first questions I'd be asking. The rest follow from there.
"A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979