Tell me what you hear when you first open the calendar.  When I open it, I
hear what today's date is.  Then I can press tab and it will say click here
to add an appointment.  You can just tab through the days until you get to
the day you want and then press enter on where it says click here to add an
appointment after the day.  Press enter there.  When you hearer title, enter
what your appointment is for.  Press tab to go through the rest of the
fields.  When you get to the change button, that is the categories list.
Press enter there, and it will give you categories you can select.  Press
the spacebar to select the category and tab to okay.  If you are having
problems doing any of this, make sure the calendar window is maximized by
pressing alt plus spacebar and then the letter x.  Hope this helps.