Buy with bank account

If you live in the USA Gemini and Coinbase are your only decent options for buying crypto with USD. I recommend Gemini because the fees are lower. Deposit money with your bank account to minimize fees.

Two Factor Authentication (2FA) and VPN

In crypto security is your own responsibility. You absolutely must use 2FA on any exchange you have money on. Write down the code with pen and paper. Read from the paper and put the code in your phone's Google Authenticator. Keep the paper backup in a secure place.

Use a VPN for added security and to hide your location. Opera has a free VPN that works well. Tor is excellent for privacy.-

Altcoin Exchange - Binance, FTX, Bitfinex, Huobi, Kraken

Binance has the lowest fees and lists many coins. FTX is a forward thinking with many indexes and perpetual futures. Bitfinex has the most coins on margin, Huobi has some coins Binance doesn't have.

Derivative Exchange - Bitmex, Bybit, Deribit, Phemex

Decentralized Exchange - Uniswap, Kyber, Paraswap, DDEX, Bamboo Relay