This article contains an example of a custom field that you can create for tasks.
You can add as many custom fields to a type, as required.
For more information, see Create custom fields.
Following is an example of a task custom field, named Priority. You can use it if you need to assign priorities to your tasks:
Apply to: Tasks
Type: Drop-down menu
Add an option and mark it with the desired colour to indicate High, Medium, or Low.
Description: Priority of the tasks
Tooltip: Set the priority of this task