Can create tasks allows you to be the author of a task. You can create, control, and close the task.
Can be an Assignee allows you to be assigned a task. You can take over the tasks and report on their completion. If this permission is disabled, you will be not included in the list of possible assignees.
Can view the tasks of all employees allows you to see all tasks in the company without being able to change them.
Can edit tasks of all employees allows you to edit all tasks and mark them as completed. (This does not work unless the "Can view the tasks of all employees" permission is enabled.)
If the "Can view the tasks of all employees" permission is enabled, the "All tasks" filter will appear on the Tasks page.