Use the note search box in the notes panel to enter your search query, then press enter. Your search term will be highlighted in any resulting note.
Use your browser's built in search functionality (typically via Cmd/Ctrl + F) to search inside your note.
In-note search is not available on mobile.
Tip: You can use the Markdown Minimist extension on desktop for dedicated in-note searching. The search box can be toggled via Cmd/Ctrl + F.