How do I declare the times that I am not available to teach?

You can declare your unavailable times on your calendar

On your tutor panel, at the top of your calendar, there is a button with the title "Not Available" which helps you announce the times you re not available to teach. When students come to your blog and look at your calendar, they will see the times that you are available. Any lessons that you have had planned in advance also shows as not available on your calendar.