I had no formal education for photography, but did have formal education in a couple of technical fields - chemistry and electrical engineering.
Like Mike, over the years I attended seminars and other photography industry related functions - like photographer association conventions.
Business skills are a key to starting and maintaining a retail photography business.
If you fail to plan, plan to fail.
So you start with a well researched and written business and marketing plan. Free business advice -
Starting a Business | SBA.gov
How to Start a Home-Based Photography Business, 6th (Home-Based Business Series)
Photography Business Secrets: The Savvy Photographer's Guide to Sales, Marketing, and More
Going Pro: How to Make the Leap from Aspiring to Professional Photographer
See the City Clerk where you live to find out what your city requires regarding business registration or licensing. It is very likely you will be required to provide proof that you have business liability insurance.
Where I live a retail business can not be run out of a home.
Your state likely would require you register with them and collect and forward to them any applicable sales taxes. You may also be required to pay state use taxes and state self-employed unemployment insurance. This is where a lot of illegal businesses get hammered - with bills for back sales taxes, plus penalties and fine.
You may be required to maintain a business bank account.
Most home owners and car insurance policies will not cover any thing you do as a business, legal or not.
For tax purposes (both sales taxes and income taxes) you will need to set up an accounting system (cash or accrual) so you can show what portion of your income is from your business.
You will need some legal documents, like a contract, model release, property release, invoices, etc.
Would you still need a license if you charged less than 100 bucks per session?
It is highly unlikely you could cover your business expenses at $100 per shoot. To make money you'll likely need an average sale of at least $300 per shoot.
Many new to doing business don't take into account all the pre and post shoot time involved. A rule of thumb is to figure that with pre and post production a 1 hour shoot takes up 3 to 4 hours of the photographers time.
Business costs are another area many new to business don't account for accurately enough and grossly under estimate what their cost of doing business (CODB) is.
Here is an online CODB calculator -
https://nppa.org/calculator