Install Gmail Notes from Chrome Web Store.
How to get started and troubleshoot this extension is explained in support note.
Notes for Gmail
Gmail Notes: FAQ (Frequently Asked Questions)
Gmail Notes, a cloudHQ extension, allows users to easily attach, and manage notes for their emails—offering options to include or exclude notes when sending messages, and ensuring integration with PDF exports for comprehensive recordkeeping.
Video: How to add annotations and notes to emails in Gmail
This video tutorial shows how to add, edit, and choose to share or keep private annotations in emails through Gmail, detailing the steps to highlight text, enter notes, and save them, along with options for editing and sharing these notes.