What is the simplest date reminder method?

[joe at actionline.com]

Actually two questions here:

(1) First, what would the PLUG brain rust suggest as
the simplest date and/or appointment reminder method?

i.e. ideally, I think I would like to have a command line
shell script where on the command line, I could just type:
$ remember "Dr. appointment Jan 25 at 12 pm" <E>

And 24-hours before that date/time, a small, bright-yellow window
would pop up on the top left corner of my desktop with that message.

(2) When I click on the digital clock on my start line,
an image like this: http://www.upquick.com/temp/calendar.jpg
appears and I can't find any explanation for why there are
different colored boxes around some dates, nor what the icon
in the lower left corner does, not what the up/down arrows in
the bottom right corner are for, nor what any other functions
of this clock do.

Where can I find some explanations?