Welcome 🤗

Zaps work on top of lightning network (LN is a layer on top of Bitcoin, but in essence it just creates and uses standard Bitcoin transactions in an interesting way).

One case of zaps is when the receiver uses lightning address (like nout@stacker.news). I have that address associated with my profile and so you will see a little lightning symbol under my notes. When you click it, the Nostr app will send a request to stacker.news to fetch a lightning invoice for "nout". Stacker News hosts my lightning wallet, so it will reply with invoice and your wallet will open and pay for it. Stacker news then sends a nostr event that confirms that the payment happened and so you can see it show up under the posts.