What is a trust? So think of a trust as a will-substitute. A will says who gets what, under what circumstances, and who's in charge of making that happen. A trust does the same thing.
The critical difference between a will and a trust is that a will has to be filed with a probate court and reviewed and approved before anyone can act under it or receive any assets from your estate. So everything filed in the probate court, including the will, becomes a public record, and, as you might imagine, it takes time to go through a public court proceeding.
A trust, on the other hand, is a completely private document. No one's entitled to see it except those who are named in it, and the successor trustee named in your trust can act immediately, without having to go to court, file anything, or get permission first. So a trust is a totally private document that can be more immediate and efficient upon someone's passing, whereas a will is a public document once it's filed with the court, and the court has to review and approve it before anyone can act under it.
So a will and a trust are similar in terms of what they're trying to achieve, but they just go through a different process down the road when someone actually needs to act. A trust is more efficient and private, a will takes a little bit longer and is public.