You will be able to see online if your region has requirements for boat owners. All who operate a power boat in Canada for recreational purposes must have a POCC, a Pleasure Craft Operator Card. Most states in the US require a license or certificate for at least some boat operators. The specifics of each program are easy to find with an online search.
You do not have to attend a boating school or take an online course. There will be periodic public courses offered in each state that you can attend. All courses will go over safety rules and tips. They will discuss the hazards you face on the water and ways to either avoid or cope with them. The rules of navigation, the use of charts, and the means of knowing your location when there are no visible landmarks will be covered. The courses also teach respect for the valuable water resources that we depend on for more than recreation.
The online courses offer great convenience, since you can do them at your own pace in your own home. This is especially valuable if, for instance, you spend your vacation in your boat in another state and it will be inconvenient to travel that far to take the publicly offered course.
Of course, each area that requires a certificate or license will have courses open to the public. These are easy to find out about online, by giving the search engine the location you need. You only need one passing grade on the exam, since the boating certificate lasts a lifetime. A fee is required to get the certificate, after you have succeeded in getting a qualifying score on the test.
Even if your home state does not require certification, taking a boating safety course is a good idea. The expense is small compared to the peace of mind that you will gain from knowing the navigational rules, safety rules and tips, and standard emergency procedures. Having a fire extinguisher and knowing how to use it might save your boat and your life. Another bonus for certified boat operators is that your insurance rates may be drastically reduced; check with your agent.
Even if you live in a region that does not require passing a boating exam, taking a comprehensive boating course may be a good idea. Your own safety, that of your passengers and crew, and the well-being of all on the water depend on your skill and knowledge.