1) When you play Buried Hoard, you may place a Coins or Hacksilver into your Buried pile, under your Deck (see page 6 of the rules for a reference).
2) When you Defend, you may place a Coins, Hacksilver or Treasure into your Buried pile, under your Deck (this means that if you played Buried Hoard and Defended, you Bury 2 cards).
3) When you Defend, After your option to Bury a card, you may attempt to Acquire a card (p.8). This means you may use the cards in your Bury pile to Acquire, or purchase, a Raid card. The cost of the Raid card equals the Raid cards Defense.
4) When you Acquire, Coin or Hacksilver cards used to Acquire are removed from your Buried cards pile, and returned to the top of their respective piles. Treasure used to Acquire is placed into your Raid pile, under your discard pile.