Absolute beginner, asking about fees

Please go easy on me, I have very little knowledge about this.

I recently received a bonus through CashApp. I’ve been looking at both CashApp and PayPal, and within the app they provide the option to buy cryptocurrency. I’m wondering if these platforms are safe to invest in bitcoin. I read in the Beginner FAQ post that CashApp charges a 3% fee, does that only apply to buying or investing? I also live in New York, do I have to pay taxes when purchasing or selling bitcoin? When I but bitcoin, am I buying “pieces” of a bitcoin, or investing in some organization?

I honestly don't get wallets or digital currency at all. I'm totally clueless, but it feels like a relevant topic to learn.

Which is the best way for a beginner who wants to trade frequently? Is it better to stick to these payment apps, or should I use an exchange like Coinbase, Binance, Strike, BYDFi, etc.? I just want something safe and easy to use.

Thanks for your advice and suggestions.