To tag a user you must grab their pubkey:

* Search their username in the search bar at the top of the 🔍 Global Feed and click their profile

* Tap the 🔑 icon which will copy their pubkey to your clipboard

* Go back to your 🏠 Personal Feed and tap the blue + button to compose your Note

* Add @ direcly followed by the pubkey

(e.g., npub1xtscya34g58tk0z605fvr788k263gsu6cy9x0mhnm87echrgufzsevkk5s)