Go to @Fountain or @Alby or @Wallet of Satoshi and grab a quick lightning address and paste it into your zap settings. You'll very quickly get your first sats (bitcoins) if you've never done so before.

All of the above are custodial, so after you start a small collection and realize how valuable they are, you can look into something like @OpenSecret or @AQUA Wallet and start down the rabbit hole of using lightning with your own keys, cold storage, and all that jazz.

That's for another day though, just grab a lightning address and I'll bet sats will start flowing in. Welcome to Nostr!