Just like any other investment, you need to find an exchange. There are more than 100 crypto exchanges on the market, but you'll need to go with a reputable exchange like Binance, Coinbase, KuCoin, BlockFi, eToro, or Crypto.com.
The exchange is here to facilitate the transaction and sometimes provide advice. Do your homework. What are the service fees, what devices are supported, how secure is the site?
You'll need to open an account and show proof of who you are. When you go to sell crypto investments, you'll have to pay taxes on capital gains.
You don't have to invest in Bitcoin. You can explore other cryptos like Ethereum, Solana, Dogecoin, and many others. But do your homework. It's a high risk investment.
Once you make the purchase, check the confirmation and set up a crypto wallet to safely store your investment. Hot wallets are susceptible to hacking and cold wallets are safest but they're not connected to the internet.