When you give someone a power of attorney, you are giving him/her the right to exercise the same power over your property and affairs that you have. For example, you have the power to spend money, sell property, cash checks, withdraw money from the bank, and enter into contracts. You can create trusts, amend an existing trust, and make gifts. Normally no one else can exercise these legal rights for you. However, you do have the right to delegate your power to someone else to do those things for you. You can do this by giving that person a "power of attorney." Granting someone a power of attorney does not limit your own rights, it simply gives the other person the power to act when or where you cannot. The person whom you give these powers is your "attorney-in-fact."
A "durable" power of attorney grants the power to act on your behalf in the event you should become incapacitated in the future. Traditionally, powers of attorney lapsed (became ineffective) when the grantor became incapacitated, because in theory you were giving someone the power to stand in your place and use only those legal powers you actually possessed. As your own powers and rights disappear when you become incapacitated, the rights you gave your "attorney-in-fact" also disappeared. Oregon has passed a law to change this tradition and allows powers of attorney to survive the incapacity of the grantor.