Open the note and run Share note… from the command palette or the note's menu.
Enter the person's email address (in a workspace, start typing a name to pick a colleague) and choose Invite.
They get an email, and can edit that note only: they don't see the rest of the vault.
Remove someone at any time from People with access in the same dialog.
Sharing a note for editing works for notes in personal vaults and needs Pro or Business. The person you invite also needs Pro or Business to open it. In a workspace vault, use access levels instead.