Tennis lessons

You are self-employed.   You are getting paid for teaching people how to play tennis.

 

https://ttlc.intuit.com/questions/2926899-how-does-my-side-job-affect-my-taxes

 

https://ttlc.intuit.com/community/self-employed/help/how-do-i-report-income-from-self-employment/00/26653

 

https://ttlc.intuit.com/community/self-employed/help/what-is-the-self-employment-tax/00/25922

 

https://ttlc.intuit.com/questions/2902389-why-am-i-paying-self-employment-tax

https://ttlc.intuit.com/questions/1901340-where-do-i-enter-schedule-c

 

 

https://ttlc.intuit.com/questions/3398950-what-self-employed-expenses-can-i-deduct

 

 

https://ttlc.intuit.com/questions/1901110-do-i-need-to-make-estimated-tax-payments-to-the-irs

 

It's a business. You are the company. It's called a sole proprietorship.

A sole proprietorship and being self-employed are two different terms for the same thing.