Dependant on your system settings, activities may be referred to as either 'Activities, Evidence or Supporting information'.
There are many types of activity
You can list all your activities by clicking on the link in the activity menu. From this page you can edit, delete or create a new activity.
From the activities listings page you can create a new activity by clicking on the 'ADD' button.
Depending on the state of the activity you may be able to edit or delete that activity.