Within nostr you can send tips to profiles and posts, which are called zaps ⚡

To send and receive zaps you need a Bitcoin Lightning Wallet. The easiest for beginners is Wallet Of Satoshi (https://www.walletofsatoshi.com/, which is available for iOS and Android). Browser users can use https://getalby.com/

To connect it to nostr you need to go into "Receive" on Wallet of Satoshi where you will see a generated lightning address (looks like an email address).

Copy this address and paste it into your nostr profile where it says "Bitcoin Lightning Address" (or similar depending on the client).

If everything worked out your profile will have a lightning bolt symbol ⚡ and people can send you zaps. Just ask around, usually someone will zap you to test it out.

There is even is a weekly event called the #zapathon where people go crazy sending zaps.