Hello bananabus & welcome to the chordie forum - It is fantastic that you want to write a song! 'What should it be about' is a great question . . . it should be about whatever strikes your imagination as 'song-worthy'.
Keep these thoughts in mind as you start writing songs . . .
* You will write more than one song (so don't feel that any one song must 'say it all').
* Keep it simple (it is just a few words and some notes - don't let it become a big, scary, difficult thing in your mind).
* Song ideas are all around us (it is simply a matter of 'seeing' the ideas and then 'using' the ideas). Ideas can be anything . . .
* Keep you ideas and observations in a notebook or journal (lots of scribbling helps the idea-seeing and idea-using process).
* Approach writing songs in a realistic and dedicated manner. It takes effort to write songs. With practice, it becomes a little easier - but it still takes real effort to be a creative person.
* "Pure Inspiration Is A Myth" Songwriting (or any creative pursuit) is mostly perspiration and just a little inspiration. It takes time to learn how to play an instrument, it also takes time to learn how to create songs. Do it a little every day. Do it when you 'feel like it' and do it when you 'don't feel like it'. If you sit on your butt waiting for pure creative inspiration to strike you, then you will never write a song because moments of pure inspiration are purely the result of dedicated creative effort.
"That darn Pythagorean Comma thing keeps messing me up!"
[url]http://en.wikipedia.org/wiki/Pythagorean_comma[/url]