You can mention your teammates on any record (candidate/company/contact/job) by adding the "@" symbol in the Notes section:

Your teammate will get an email notification with a link to the record you mentioned them on. If you are on the Business plan, you can also mention "Teams" as well.
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​Important Note: They might need to mark this email as "Not Spam" the first time so that all future "Mentions" show up right in the inbox.

You can reply to this email directly to start an email thread with your teammate or you can click on the "View Mention" button to be redirected to the record where this mention was added.

You can see all "mentions" in the Notes section:
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Hope this helps!

Other articles that might help:

Happy Recruiting :)