I will ask for information about your focusing. That information is used only to help you. No one else looks at that information. No other information is collected.
A cookie is used to recognize you, so when you are halfway through your focusing session, I can connect you to the information you have already given me. Think of it as a way of making your computer unique, so that I can tell the difference between you and someone else's computer.
That creates two potential problems.
Tell me about the problem of storing cookies
Tell me about the privacy problem