Monsters will randomly drop coins upon death. You can also find coins in chests. To add the coins in chests to your currency counter you need only right click whilst holding them, and they will be added. Alternatively, dropping them and picking them up as any other mob drop works just fine. There are 4 tiers of coins: bronze, silver, gold and platinum. These can be used to trade with villagers. Coins will currently upgrade themselves. Upon collecting 64 of on tier of coin, it will automatically be converted into 1 unit of the next higher tier. This is a placeholder value and is to eventually be changed to 100.
Currently, only a maximum of 63 platinum coins can be held. Money gained in excess of this will be lost. If the player's money total is incremented to exactly 64 platinum and 0 of the other three types, future money picked up will be added to the inventory, rather than removed from the game like normal.
When you find a NPC village, right clicking on a non-farmer villager (one that has an apron of some sort) will open up the trading GUI. At the top of the GUI there is a box with the items that the villager has to offer, and underneath is your inventory. Hovering over a villager's item displays its price to purchase, and hovering over one in your inventory displays how much the vendor will pay for your item. Currently the villager's type does not affect the items, although the selling and buying rates do vary from vendor to vendor.
Village spawn rate has been increased so that they can be found more commonly. However, as with vanilla Minecraft, villages may only spawn in certain kinds of biomes. The villagers that spawn inside the villages will be given a first and last name, along with the appropriate level.