Adding and managing tasks are very easy
Click on the task tab on the sidebar then write in the task that you want to add.
Add the task item
Click the + button
To delete the task, just select the task you want to remove and then you will see the X, click the X and the task will delete.
Tasks a global and not associated to a specific lead.
Only you can see your tasks.
You can drag and drop the order of the tasks as you require.