The Timeline in the contact summary stores a log of events or activities for that contact, including emails to and from, notes, reminders, and contact actions (e.g. opening an email). Simply click on a contact to see their timeline.
When viewing a contact's timeline, you can filter what you can see. If you want to see emails sent to or from, notes only, or reminders only, you can select it from the drop-down menu.
Note: The default timeline view is Reminder & Notes.
You can also see a contact's history from the Contacts Dashboard. Simply click on the Last Activity icon (), then click View More Activity, and you'll be able to view the timeline for that contact.