Aikido means different things to different people (and at a different periods in your training). It is common to start Aikido as a self-defence, though other aspects become apparent.
One thing you'll learn, for instance, is that pages and pages of words are no substitute for experience. Best thing is to go along to the dojo and see what it is like, and also try out other martial arts and see how you enjoy them. I've never known any dojos to require a commitment to long term training when you start.