A Will is a simple document that outlines what happens at death. A Will allows you to specify who gets what, but allows for little customization as to when and how assets are distributed.
A Trust is a more sophisticated document that can apply during your lifetime and after your death. A Trust allows you to specify who gets what but also allows you more control over when and how assets are distributed – a great feature for those with younger kids.
One important note: Wills go through probate. Assets held in a Trust will avoid probate.