There are many ways to play all the different mods. "sparring" is normally when two people play to make a "realistic" fight. You can see examples of these in the default replays like " Swexx vs Largekilla"
Mods are different based on reaction time, frame rate, and other things like gravity and possible weapons, and obstacles.
Judo is a good introduction mod because it has low gravity and big frames. Aikido requires a little more knowledge because the frame rate is much smaller, giving you more opportunity to fine tune your moves.
Remember this is an old game so there is a lot to learn. I recommend picking up all the technique you can in judo as you learn what each individual joint does. After that you need to watch other people play.
http://forum.toribash.com/showthread...=460415&page=2
This is a link to a thread about how to start a match. (The tutorial board also has very detailed guides for different mods.)
I really want to emphasize how important it is to know what each little joint does. The better you understand how movement is created the better you will be at playing different mods.
If you find me in game I can help you.