"Never spend the “corpus” (also known as the capital) you were left. Steward your assets to leave even more to your children, and then teach them to do the same. And finally, use every tool at your disposal within the law, especially through estate planning, to keep as much of that money as possible.." -Abigail Disney
Every state has some default set of rules that happen whenever you die. They may or may not be useful for your particular situation. Usually it goes through a process called Probate, where the courts help determine where everything goes(i.e. Tootie gets the house and Tito gets the bank balances, etc). A person called the Executor is in charge of that process. A will is your written declaration of all of this stuff.
You probably don't have to do any of these things, at least for most of the larger assets. There is a beneficiary designation you can do, which will magically skip courts and probate and just change the ownership. This works for Houses, Banks, Brokerage and retirement accounts and most pensions, etc. Houses are done via a "beneficiary deeds" or "transfer on death deeds". Vehicles can be done in some states, but most are not quite setup to do that yet.
The next thing is a Medical Power Of Attorney(MPOA) and a Financial Power of Attorney(FPOA). An MPOA is the person legally allowed to make medical decisions on your behalf if you are unable to do so (unconscious, coma, etc). In my state, there is a couple of pages of form you fill out , have notarized and give a copy to your primary care doctor and to your MPOA. Your state may be different. I recommend starting with the American Bar Associations page here and the form that I used, that worked in my state is here.
A FPOA is the exact same, but authorized to handle your financial decisions(i.e. pay your bills if you can't) if you are unable to do so(coma, etc). It's not quite as easy as an MPOA, since every financial institution usually has their own stupid form(s) AND you probably need a state authorized version for the court(s), just in case they have to go through the court system to get a bank/brokerage to behave, if they decide last minute they didn't like the forms they made you fill out.
Generally it's advised they are not the same person for obvious incentive reasons. Every state will have a default, legally codified ruleset for this, that may or may not make sense for your particular situation. You should research what your state's laws are around these 2 things and then see if you are ok with them or not. I was not ok with my state's laws, so I had to do all this paperwork. Not that it hurts to do the paperwork anyway :)
What I do is let everyone important in my life know my wishes, I have it in my calendar to touch base with them every year about my wishes. I let them know my Medical Power Of Attorney(MPOA) and I let them know my Financial Power Of Attorney(FPOA). I also let them know where all my assets are going when I die(which also happens to be my FPOA.
I don't want it to be a surprise, I don't want anyone to wonder about what I wanted to happen after I'm dead.
A digital "death box" also exists: https://www.fidsafe.com It's totally free and ran by Fidelity(A brokerage with trillions of dollar of assets), so they aren't going anywhere anytime soon.
I don't use it, because my MPOA and FPOA know my wishes, and I touch base with them every year and let them know if anything's changed. I just send them an email. Also, I let my loved ones know all this stuff. I try to tell them once a year, who my MPOA and FPOA is, my general wishes, etc. I don't want anyone surprised.
Trusts
You might not need one, but you might. I don't have one. See the PDF "Anatomy of the perfect modern trust" and part 2