Choose two cards, including a matching pair
You may choose two different resource types or two of the same type. Taking wood and brick can pay for one road; taking two ore may complete a city hand that already contains one ore and two grain.
The effect adds exactly the chosen two cards. It does not automatically build anything, supply a missing road connection or waive the ordinary placement rules. Plan the purchase you will make after receiving them.
The bank must be able to supply both
If you choose two different resources, the bank needs at least one of each. If you choose a pair, it needs at least two of that resource. You cannot draw a card type that is absent from the bank.
This differs from Monopoly, which collects from opponents. If the bank is short of ore because players are holding it, Year of Plenty cannot simply take those cards from their hands. Consider a different pair or a player trade.
Solve the narrowest bottleneck
Suppose you have wood and brick, a legal connected settlement site, but no wool or grain. Choosing wool and grain completes the settlement without surrendering the resources you already hold.
If you are still three roads away from the site, that same pair does not finish the plan. Count the whole remaining cost. Choosing cards for an immediately useful action is often stronger than adding resources that merely look scarce.
Keep the card timing in mind
An action card bought this turn cannot be used until a later turn. You may play only one action development card per turn, even if you hold both Year of Plenty and Road Building. Do not plan a same-turn combination that the rules forbid.
When the card is eligible, compare using it now with keeping flexibility for later. A certain point or a contested settlement can justify immediate use; a speculative hand with no legal next purchase may not.