Hello SK290,
Most of us that picked the sport at an early age started as freedivers and the use of the speargun became just an extension of the arms, as we got older, wiser and deeper the use of the scuba became just another tool to get at bigger/better targets and it’s been the same since for the Hard Core group.
If you’re interested in this sport and you’re including scuba to the mix you need to become a "good diver" with lots of open water, reef and wreck dives first then check in your area for local laws for permits, fish size/limits and very important fish ID for the sites you’ll be hunting.
To start you will need a small to mid size gun around 36" to no more than 48" long with two or three slings ( three is better) a rock tip for reef or wreck hunting and a fish bag, wire or hanger to keep your dinner secure after is shot.
It takes time to become a good speardiver or scubadiver but it takes longer to be good at bouth.
Start in the shallows with good vis. no current and as you learn the "tricks of the trade" you may want to get into deeper sites even with time and experience get into some Blue Water stuff but that’s another animal all together.
There are many books on the market and you can also check with your local diving club to see if they have other members who spearfish and IF they’re "spearfing friendly" many are not so check into this first. There are many diving clubs/divers who do not like blood or killing around them! Just a heads-up!
Best of luck to you, if I can be of any help just ask.
Spearo.