The Shop allows you to buy Gems (for money), and coins (for Gems). Gems are the main currency in the game, and are used for Temple Summons, Revives during quests.
Sometimes, the Shop will feature bundles, which offer extra value. These may include Gems, Coins, Summon Tickets (one Summon Ticket gets you one Temple Summon) or Ales.
There is a Starter Bundle available - only once - which includes all of the above.