There are four buttons that are shown to the right of each activity in the activity feed.
Charge an Activity Once
This is used when you have a contact you are unsure if you have ongoing work with, however you want to charge this specific activity. All future activity from this contact will continue to arrive in the activity feed for your consideration.
Delete and Activity
Like Charge Once, this is also used for a contact you may/may not have ongoing work with. In this instance you will delete this activity but will consider whether to bill the next. Future activity from this contact will continue to arrive in activity feed.
Charge and Upgrade an Activity
Use this for a contact you regularly do billable work for. This ensures all activity going forward from this contact will appear as a time entry in your timesheet and be matched to the last matter you billed them for.
Delete an Downgrade an Activity
Use this for a contact you will never do billable work for. (For example, personal contacts or colleagues). This function effectively archives the contact and their activity will go to the deleted folder. If you later do billable work with them, you can reverse the classification.