Ok. Rewinding here, we're going through the basics.
SO WHAT IS NND?
NND (NicoNico Douga) is basically Japanese YouTube. It started as a way for Japanese people to watch YouTube videos, but then it kinda sorta evolved. WHOO! Now on NND, it's possible to watch videos, comment, subscribe, etc, all that YouTube stuff, and you can watch live broadcasts.
On NND, you can "mylist" a video (favorite it), favorite channels, users and communities, and follow these users. However, you have to be careful because unless you are a premium member, you do not have unlimited space to do so. Premium membership grants you more space to favorite and follow, and it also allows you to do things such as enter a live that already is full (if a live gets too busy, they will stop letting users watch since it slows down the whole thing).
On a random note, unlike YouTube, the things you comment on NND appears on the screen as subtitles. It's kind of cool, but it can get annoying. No worries though, you can always turn it off.
NND also has gone MOBILE (omg what) There's both an Android app (https://play.google.com/store/apps/details?id=jp.nicovideo.android&hl=en) and an iTunes app (https://itunes.apple.com/us/app/niconico/id307764057?mt=
. The iTunes app is in Japanese, so you may find yourself clicking around blindly, but the Android app is mostly in English. These apps allow you to watch videos and lives on your mobile device.
Here's a page full of NND terms you might want to familiarize yourself with: http://utaite.wikia.com/wiki/Nico_Nico_Dictionary
There's lots of slang on NND. You have things you're probably familiar with (ikemen, bishounen, bishoujo, etc). You have things that also translate to English typing slang, like wwww (which means LOL with varying degrees of LOOOOOLness).
There's lots of different type of video makers, just like there are on YouTube. You have the gamers, the makeup tutorials, and all that stuff, but you also have a HUUUGGGEE COMMUNITY OF ODORITE (dancers) AND UTAITE (singers).
So really, go check out NND. It's pretty cool. http://www.nicovideo.jp/