I got up to rank 7. MLN shouldn't count as a social networking site. The only way you can communicate to others through it is by soulless preset messages. It's closer to a puzzle and teamwork game, where you gather resources through various ways from NPC users and secret NPC users.
Like a social networking site, you have your own page, on which you can place modules. Modules can receive clicks from other players. Advanced modules you gain later on allow you to gain specific resources per day, and/or resources per clicks. Clicks are limited though, as each user only gets a specific number of clicks per day. Users have 20+8*rank clicks to spend each day, that accumulate evenly across the day. Rank is determined by the number of masterpieces you have made. Masterpieces are made from gaining a masterpiece blueprint, and gathering the resources the blueprint states. Each rank, from 0-9, has a masterpiece to go to the next rank, so there are ranks 0-10. Rank is the primarily a status symbol in MLN.
Each rank has its own NPCs that will only friend you at that rank. By friending an NPC, you can trade with it on its page, or send it mail for hints or items.
There are a wide variety of resources in MLN. The most basic are bricks. You start off with red bricks, but eventually have to deal with blue, yellow, green, purple, orange, black, white, grey, and clear bricks as you advanced in rank. You also have to gather an odd variety of items to complete blueprints for masterpieces, modules, or items. Items or resources are also required to click on specific advanced modules.
Modules give you plenty of options of how to set up your page. Your page is a 3x4 area, and modules take up either a 1x1, 1x2, or 1x3 space.
The main goal of MLN is to get each rank and masterpiece. You can also attempt to friend secret NPCs, or side plots that don't deal with rank, such as the Bionicle Plot.
The higher you go, the more complex it gets, and the more teamwork you need. By rank 5 I needed to make a bot to continue, as I was forever alone. Also, I seem to have gotten carried away with this post.
I would be interested in working with a team to get to rank 10.