At least at first, all characters come from Sandpoint, a small town in the country of Varisia, see the Jade Regent Player's Guide for details.
As the campaign has now left Sandpoint, your character is someone who travels with "Koya's Final Caravan". If you have a really good idea for someone who comes from the area the campaign is currently focused on I'll probably allow it.
When creating the character, see the Character creation rules. The campaign used 'Epic Fantasy', but once any player changes characters the campaign will switch to High Fantasy, meaning that all characters will have change to using 20 points.
The player's guide can be found here: