The approval and rollback activities, as shown here, are available only for tables that extend from the Task table. If the table doesn't extend from the task table, then all the activities except Approval - User and Approval Action are grayed out and not available:

The following different activities are available under the approval and rollback activities:

• Approval Action: This activity is used to perform an approval action on the current task and mark the task as approved or rejected.
• Approval Coordinator: This activity is used to create an approval whose result depends on the output of one or more child activities, which usually includes one or more of the Approval - User, Approval - Group, and/or Manual Approval activities.
• Approval - Group: This activity can be used to create approval requests for each member of a specific group.
• Approval - User: This activity creates one or more individual user approval request. We can specify whether the request will be approved if one of the selected users approves, if everyone approves, or run a script to determine the outcome.
• Generate: This activity can be used to create task or approval records from any task or approval activities placed after it. If the Generate activity is not used, the workflow engine waits to create any records until reaching the associated activity during workflow execution.
• Manual Approvals: This activity watches any approvals that are added manually outside of the workflow process. It basically monitors the status of the approval field.
• Rollback To: When the Rollback To activity is triggered, the workflow moves processing backward to a specified activity in the workflow and resets overlapping activities that have already executed back to their original state.