A Will is a piece of writing, signed by someone with the intention of directing the distribution their assets on their death, and also signed by two other people who have, together (not individually), seen the first person sign the writing.
At its most straight-forward, a Will should name someone to have authority over the deceased’s assets (an Executor) and someone to inherit them (a Beneficiary).
From that, much argument has flown and a great deal of law, both found and made, has grown up. If you have a plan in mind for your estate on your passing that has any level of complexity at all, please seek advice.