Tasks work best when they are added to bookings and contacts. For example on the booking page in the sidebar you can open the form to add a task. This will add the task to your task list but, importantly, it will be followed by the booking name and date. This will make the task much easier to keep track of for all members of your team.
You can add a name for the task and in the due date dropdown you can select a specific date to see a date picker. You can also give your tasks a specific category. If you would like to choose a category that doesn't exist you can add these in the settings.
You should think about setting up your task categories as early as possible so that all members of your team can use them as you require. If you head over to settings and then in the sidebar go to tasks. Click the Add Field button each time hitting enter to save. You can also see here that you can setup some default tasks to appear for each new booking if you have tasks that you always create it's a good way to automate that process.
If you head back over to the tasks tab and find a task you can see if you hover on the task, a menu appears to the side. You can either edit or delete the task. Click the pencil to edit and see the task from where you can make any changes you require.