The ratings are based on the ELO rating system (
http://en.wikipedia.org/wiki/Elo_rating_system) and (
http://en.doc.boardgamearena.com/Rating), with some adaptations.
First, before all the gory details I'm about to explain,
don't worry if your rating doesn't match your opponents' ratings. The ratings are a
guide to the skill of the player. Most people don't find it fun to play a game if they get defeated soundly. Likewise, most people don't find it fun to play a game if their opponent offers no challenge at all. Then again, some people want to see how the experts play so they can improve their own play, and sometimes people want a relaxing game where they don't have to over-analyze every move.
Basically, everybody starts off with 1500 points. When you win, you take some points from those that didn't win. How many points depends on how big of a difference there is already: A low-ranked player beating a high-ranked player will transfer a lot more points than a high-ranked player beating a low-ranked player.
Now, that number is converted to a range.
- Beginners < 1400
Average level 1400-1600 <<--- This is where one begins their first game.
Good players 1600-1800
Experts 1800-2000
Masters > 2000
(I think these are accurate -- I could only find numbers for good, expert, master in the BGA documentation.)
Anyway, it means that if someone is listed as "good player," they either regularly win against average level, got a couple of lucky wins against an expert, or won a lot of games against beginners.
It does not provide quantitative information about how fun it is to play with them. Again, most people like playing with someone near their own skill level, so there generally isn't a table with masters and beginners on it. However, there are often tables with beginners through good, average through expert, and good through master (based on what I've seen).
When creating the table, the administrator can restrict it to the listed groups, in any way they want (even making it that only beginners and experts can join, if they wanted to). If the administrator didn't put in a restriction, they are claiming they don't care what levels play. Anyone joining a table knows the restrictions (or lack thereof), and likewise claims they don't care if someone of an allowed rank joins. When joining a table, one can also see the ranks of those already present, so can decide if they want to play against that skill level. If it's open, feel free to join.
Now, some side notes:
These forums are full of threads about how the ELO system is broken as implemented on this site. That's true. It's a guide, take it as you will. There are some people that treat this site as a game in itself, and feel they must attain the highest score possible by exploiting loopholes in the rules. I tend to think these people are the minority.
This site draws people from all over the world. People tend to be good at what they enjoy. If they enjoy a particular game, they tend to be good at it. The majority of players are playing games they enjoy. This means that the majority of the players on any particular game are going to be better than a random sampling of people in any gaming group. For example, you may play physical games with Alice, Bob, Carol, and Dave. Alice wins worker placement games, Bob wins resource management games, Carol wins card games, and Dave wins set collection games, but they all play all of the games. On this site, I've found that I run into a bunch of Alice's on the worker placement games, a bunch of Bobs in resource management, tables full of Carols holding cards... That isn't to say that they don't play the other games; it's just to say beware that even average (and beginners) on this site may be more skilled than the general physical population around you.
Still reading? I'm impressed. Final thought: Play games, and have fun. If the table doesn't say "newbies need not apply," pull up a chair. Who knows, you may run into an expert who wants others to enjoy the game so will patiently explain subtleties of the game that are often overlooked.