There is no reason to be scared of sharks as long as you don’t encounter them.
More seriously now. The best place to start is taking a freediving course and get familiar with the dangers of shallow water blackout and how to avoid it. You will learn about relaxation, equalizing your ears, dive technique and much much more. The things you will learn are priceless and will keep you from going out by yourself trying to figure things out and potentially dying.
Swimming is great training for freediving and spearfishing so go ahead and get in shape.
When the freediving becomes second nature it’s time to get familiar with your local waters and understand current, tides and suitable spearfishing conditions.
Ideally you find someone to learn from. If not go slow and remain safe. Don’t dive alone.
Going slow also applies to hunting technique. When you think you’re going slow, slow down even more.
Start listening to the NoobSpearo Podcast. There is a wealth of information on there.
Search the forum and ask questions.
There must be local spearos where you are so connect with them, stay humble and they probably teach you all you need to know. It can be a steep learning curve, enjoy the journey.