Queue is used for fulfillment activities, so queue tasks are any activity that takes place as part of the fulfillment of a request. This can include approvals as well as what are generally considered fulfillment activities.
Queue tasks all have assignment. They can be assigned to a team and to an individual within that team. You will have permission to reassign, view, and grab (assign to yourself) any queue task in a team you are a member of. You can only work items that are assigned directly to you.
Note that you do not need to be assigned a task or in the group assigned a task to be included in the discussion on that task. You will still be able to see the discussion on the space/solution home page and you will still receive notifications for the discussion even though you will not be able to see the task itself.
Whether an approval or fulfillment task, you can only work items assigned to you directly. When you initially view a queue task, you see the summary and details of the task, a button to view the originating request, any associated subtasks, and the associated discussion (if any). The Status field, approval decision, resolution notes, and any custom fields are only displayed once you click the Work It button.
Note that the summary and detail fields of the queue task are text fields and cannot display HTML. Any HTML you wish to pass to the person working the task would need to be either in the original request or in a custom element in the Work It portion of the request.
There are a few preconfigured queue tasks, including an approval and a tasks (work order). These can be used as is, but are also meant to be used as templates to create the specific needed approvals and tasks used by your company's processes.