First things first!
Firstly, ensure you have the app installed into your outlook client.
If you do already – you will see the Dynamics 365 icon on the Home toolbar in Outlook:
If you do not have this, see the ‘How do I get the new CRM App for Outlook?’ section on https://blogs.msdn.microsoft.com/crm/2015/12/10/the-new-light-weight-crm-app-for-outlook/
To track an Email or appointment first select it. For an email select it in your inbox, for an appointment open it up out of your calendar.
Once selected then Click the the Dynamics 365 icon on the Home toolbar in Outlook:
This will open a Dynamics 365 Pane in your Outlook Client which will displace contact details of the email recipient.
You will also see a blue TRACK button (highlighted in screenshot above).
Click the TRACK button which will then bring up a search bar.
You may use this to search for the record that you’d like the email/appointment to be set regarding and click the record in the search results to do so.
Once done the email/appointment will be visible under the activities tab on the regarding CRM record.