From within an activity, in the History summary section, it is possible to create 'follow-up' activities. By default the current activity will be ticked as complete, but it is possible to de select this:
If you have created one or more follow-ups you can track these, and access them, via the ‘follow-ups’ tab on an activity record. This tab is only visible if the activity has related follow-up records:
The current activity is also displayed by default, though this can be de selected to hide if this is confusing.