From the Super Mario Wiki
The Trouble Center (spelt as Trouble Centre in the PAL release to match the British spelling) is a building found during the events of Paper Mario: The Thousand-Year Door, located in East Rogueport. Inside the building is a bulletin board where various characters will post particular troubles that they need someone's assistance with, such as bringing someone a requested item or making a delivery. Once Mario successfully completes a trouble, he will receive a reward. These rewards are determined by the person who posted the trouble, and range from different amounts of coins to specific items.
Troubles are sidequests, much like the favors that Koopa Koot recruited Mario for in Paper Mario. However, rather than completing the troubles in order, Mario can pick and choose the troubles he wishes to do from a list. Every time Mario completes another chapter, more troubles will be added to the list.
Troubles are completely optional, as Mario can finish the game without setting foot in the Trouble Center, although he will miss out on several good rewards if he does not. Completion of all troubles yields no special reward, so it is possible for the player to pick and choose which troubles they would like to complete, while omitting the more tedious or undesirable ones.
When Mario takes on a trouble, there is no time limit for when it must be finished. However, Mario can only take on one trouble at a time, and canceling a trouble he signed up for will cost him 30 coins.
Names in other languages