There are 4 currencies, gold, silver, honor and paid gold all of which can be used in the shop.
Honor is earned at the end of each week(Tuesdays) depending on your rank in PvP arena. You also earn honor for your overall rank and being in the top 1000 for either 1v1 or 2v2 PvP.
Gold is a currency earned through Devotion Quests, as random drops in campaigns, PvP and dungeons, through achievements and given with honor based on your rank. It is also earned by completing achievements and events.
Paid Gold buys all the things gold does except it isn't dropped anywhere in the game and you have to purchase it with money or digital currency (such as kreds for the kongregate version). Regular gold will always be used first when paying for an item or action that requires gold.