NOTE: You will not be able to see this sign once you reach level 6. To see all of the commands available here, do 'look plaque'
The Adventurer's Guild is where you come to get Advancement Points by spending your experience points. Advancement points (adv points for short) can be used to train stats here (strength, intelligence, and so on), or to advance levels at your guild (you can't advance levels here). It always takes exactly four (4) advancement points to advance a level at your guild. Training a stat takes a variable amount of advancement points, depending upon your race; use the command 'list stats' to see how much.
You probably shouldn't do stat training until you are at least level 15 to 20. This will make getting advancement points later more expensive, and besides, just getting advancement points will sometimes increase your stats (according to your race) and advancing a level in your guild will sometimes increase your stats. To get an idea of how quickly the cost of advancement points rise, use the command 'list adv'.
Once you have decided to advance a level, you should get the four required advancement points as soon as possible, rather than waiting to get enough experience points to get the advancement points AND to advance at your guild. Why?
Because, if you die, you will loose a portion of your unspent experience points, but you won't lose any advancement points, so any experience spent on advancement points is safe.
NOTE #2: It's a good idea to read 'help newbie'.