A California will is a document that provides for transfer (or distribution) of your assets at death. It picks up all of your assets that are stuck after your death and it says where they’re to go. The could say those assets go to:
Of course, you make the decision of where those assets will go.
Stuck assets are assets that remain in your name at your death that you have not setup to transfer automatically to another person at that time.
Without a will your “stuck” assets will go to your heirs after your death. Your heirs are your closest living relatives as defined by California law. That works fine for some people, but not for everyone.
Normally a will also states who’s to be in charge of carrying out these transfers, and that person’s known as an executor. You also make the decision about who’ll be the executor.
By the way, the person who signs a will is called a testator. That’s you.
A will does not do anything until your death. It has no effect until that time. Therefore, it does not help with making sure that someone you know and trust will have the legal authority to take care of you if you can’t take care of yourself anymore in the future for some reason. You would need a trust, a power of attorney for financial management, and a power of attorney for health care to do that.
Further, a probate decedent’s estate court proceeding may be necessary at your death, even if you have a will. Most people want to avoid the effort, delay, fees and other expenses of a probate decedent’s estate court proceeding.
There are ways of avoiding a probate decedent’s estate court proceeding, and a will is not one of them (but having a properly setup trust is a great way to avoid that).