How do I get a physical address for my online business?
Congratulations on wanting to start your own company.
There are loads of places where you can rent a mailbox and get a street address. The first place that comes to mind is The UPS Store. You can visit their website, input your zip code and find the closest location to your home. If there isn't a location near you, do a web search for "mailbox rentals" + "your state" and I'm sure you'll find something close to you.
It's also a good thing to do to keep your business affairs separate from your personal life and maintain your privacy and security at the same time.