In your will, you can deal with property you own solely. You do not need a will to deal with property that you own jointly with another person. For example, if you own a family home or a bank account jointly with someone else, that property goes to the other person when you die. Anything you say in your will would not affect property you hold jointly with someone else.
Your will also will not cover any property that has a designated beneficiary. For example, if you have life insurance, and the proceeds go to someone you named in the life insurance policy, your will does not affect how the life insurance proceeds will be paid.
Please see the Creating a Will Self-Help Kit for more information.