A will, or testament, is a legal document that expresses your wishes as to how your assets are to be distributed after your death.  It also will state who is to manage the assets until their final distribution.  if you have children, by having a will, you can also plan for their future care and provision.

A power of attorney, or POA, is a legal document that allows you, the principal or grantor, to authorize/appoint someone you trust, the agent, to represent you in conduct your financial and legal affairs in event that you become incapacitate or unable to act on your own behalf including if it is due to old age and/or illness. 

Representation agreements, similar to POAs, allow you to appoint a person you trust represent you in handling your healthcare and personal care needs in accordance with your wishes. This will provide you with some peace of mind by knowing that a trusted individual of your choice can speak on your behalf with doctors or other professionals in the medical and personal care industry should you become unable to express yourself due but not limited to old age and/or illness.

Advanced directives are your way of legally stating how you would like your  end-of-life care handled, in advanced, in a legal document format for others to know and follow.  This is a way to tell your wishes for your final moments to family, friends, and health care professionals and to avoid confusion later. This can include do not resuscitate (DNR), Physician Orders for Life-Sustaining Treatment (POLST), organ donation, and more.