In Contact Details, press on the Activity tab.
Comments function as internal notes for you and your team to refer when necessary. For example, you may include some long notes regarding an issue or situation in the comment instead of a custom field.
Comments are tied to the contact and visible across the space. Anyone who view the contact details will be able to view the comments too.
As a mentioned user, you can simply hit the Reply from the comment to reply to the user who mentions you. This feature simply adds the user's name to the comment for ease of use.
Any conversation events that are triggered with this contact will be listed in Contact Activity too. Refer to Conversation Events to learn more about the events triggered.
The Conversation Events are grouped according to their dates and sorted from the latest to oldest. This way, you can run through the events that has happened to a Contact when necessary.