most of the courses you'll see promising to get you your captain's license work toward helping you pass the test, that's all. The test is a written test. As for your time on the water, you'll need to prove it by either getting another captain with a charter business or ferry operation etc to sign an affidavit testifying as to your time on the water, or you can sign one yourself if you own the boat. You'll need 360 documented days on the water before you can get your OUPV or 6 pack license - which will let you take 6 passengers for hire on your boat.
That said, true experience is about much more than the numbers. You need lots of real world, boat handling experience, in different conditions. Not to sound dramatic, but you'll have people's lives in your hands. Lots of little mistakes can be made on the water with big consequences.
then there's the fishing. You have to get it REALLY dialed in. Are you looking to do light tackle fishing, or trolling etc? Two different markets and very different customers. Where are you looking to launch out of?
I started a charter business 12 years ago... my day job gets in the way these days, so it's really tough to keep a regular schedule so I don't do it much. I really liked doing it, but it's a lot of work.
You need to really dial in your boat handling before. I've seen a few bad things happen out there.
Try a 'seamanship" school before a "captain's school." They might give actual boat handling tips.