A will serves as a map for the court to follow. A will tells the court who you want to administer your estate and what you want them to do. With a will your assets still must go through the probate proceedings.
A trust is completely different, more protective, and private. A trust creates a legal entity that holds your assets, and if done properly, can avoid probate court involvement. The trust takes control over assets you select either before or after you die, and distributes them according to your instructions. There are several different types of trusts useful for different situations.