The Availability page is a calendar that you get to by selecting Personal > Availability.
The blue coloured day on the calendar indicates the current date.
Green bars indicate that you are available, and red bars indicate that you are unavailable.
A bar with the circular arrows on it indicates that the entry occurs more than once within a specific date range.
You can click an entry to see more information about it.
If you click the blank area on a day that already has an entry, the Add Entry pop-up will appear, instead of the entry details shown above.