Cards are tasks and they represent work deliverables, and you can organize them just as you want. Cards consist of the lowest granular level of your project details. This is where all the action takes place. You can create cards or deliverables inside lists for any board/projects. You can then assign them to team members and set their due dates, start and end dates. You can also move tasks horizontally from the left List (start of the process) till the right list (end of the process), using simple drag and drop operation.
Further, you can track the progress of the task, view and set due dates, add comments, add tags, and so on.