You likely have checklists that have been created and used outside of Karbon. Whether it be in Excel, Google docs, CSV file or on virtual notepad, you can simply copy and paste the checklist into Karbon, and turn it into a list of tasks or client tasks.
Just select the data you wish to copy, perform a copy function (Command+C or Ctrl+C), select an empty task list item row within Karbon, and do a paste function (Command+V or Ctrl+V). Karbon will ask if you would like to keep the data as one item or split into several items. Choose Split and Karbon will magically re-create the checklist into Karbon as a task list.
If you wish to create client tasks, simply follow the same steps, but paste the tasks into an empty client task.
However, when doing this, you can only copy and paste the task list item names. You will need to later add in one by one the descriptions, to-do date, and end dates if you have them already available to copy.