A Will or Last Testament is a legal document where a person puts into writing their wishes for the care of their belongings (Estate) after they pass. It is a way to insure who will receive the bounty of all your hard work. It is also a way to insure that the state or government does not have a say in how your belongings will be divided.
If a you die without a Will (Intestate) then the state statutes will decide how your belongings are divided. For example, if you are married with children. Your spouse only inherits half (1/2) of your Estate and your children inherit the other half. If you are not married and have no children, your siblings and parents may divide your Estate.
A Will can establish who will be the guardians of your children. This is the person who will take care of your minor children. They should be a person who you trust to take care of nurturing your child, raising them as you would and becoming the loving "parent" in their lives.
A Will can designate items to be given to a specific person(s). This can assist in transferring family heirlooms, or in the case of a blended family, that a specific child is left an item from their respective parent or family.
This is an even better reason to have a Will in place. If there is property of any kind to take care of, a person designated by you is a great asset to the Court in closing out your Estate. A close friend can be the Executor or Representative of an Estate.