The website is basically a social media website for moviegoers. I found it about a few months ago and absolutely fell in love with it.
You can use the site to track which movies you've seen in a diary, rate them out of five stars, and also write reviews. You can also create lists (Top 10s, Genre Specific, etc.) and have a watch list. You can follow other users to see the movies they see and their ratings/reviews.
I have MoviePass and am a film major, so I got to the movies or see movies a lot. It's a nice way to keep track of the films I've seen and I actually write reviews for every movie that I've seen.
Here's my profile if you want to check it out. There's a pretty small user base but it would be a lot more fun if there were people I could follow!
I just created my own today, but I think it will take a lot of time to flesh out my profile. I've seen so many movies and regularly watch a lot too, so it'll be difficult to fill out my film diary, but I'll take it little by little I guess. I don't want to review too many movies too fast or else I'll just speed through it Follow me! http://letterboxd.com/shappyrohman/
Yeah it can be pretty daunting. I'd suggest looking at the top films from each year (there's a section on the website for that) and then starting from there. That's where I got a chunk of the films I have on my profile. It's not entirely necessary though, and one of the best parts is doing a diary of films you've watched this year, which you can just start with now. I followed you, and look forward to reading stuff from you on there!
The social aspect is such a minor function of the website. The social aspect boils down to find people who have good taste, or similar taste to you, or who analyze movies in a thoughtful way so you can see what they watch/like/review and get ideas for what youd like through that. You dont even have to use those functions though. I mostly just use it to keep track of what movies I've watched and find new movies and make watchlists.
Honestly there's not a lot of people on the website, so you could completely ignore the social aspect and it's still pretty useful for logging the films you watch, etc.