To use your checklist, simply work your way through it in order, dealing with the A priority tasks first, then the Bs, then the Cs, and so on. As you complete tasks, tick them off or strike them through.
But in you’re in an operational role, or if tasks are large or dependent on too many other people, then it may be better to focus on a longer-term checklist, and "chip away" at it day-by-day. Many people find it helpful to spend, say, 10 minutes at the end of the day, organizing tasks on their list for the next day.
What you put on your checklist and how you use it will depend on your situation. For instance, if you’re in a sales-type role, a good way to motivate yourself is to keep your list relatively short, and aim to complete it every day.
You may find it easier to compile several checklists (covering personal, study, and workplace, for example). Try different approaches and use the best for your own situation.