Onigiri is a Japanese lunch staple. Most non-Japanese know it as rice balls. It is easy to prepare and easy to pack. I personally don't really like umeboshi or meats in my onigiri, so I make it this way.
Cook the rice either in a rice cooker or in a pot on the stove. Ratio of rice to water is 1:1.
While you are waiting for the rice to cook, shred up the nori if it is still in large sheets, or small strips. You want to be able to distribute the small pieces through the rice.
When the rice is done, stir it up. Then take half of it and put it in a bowl large enough for it to be mixed around inches.
Add 2 teaspoons of sesame seeds and 2 teaspoons of nori and mix to evenly distribute.
If you have a mold, put the rice into the mold, press and plop out onto a plate or saran wrap to wrap it inches If you don't, wet your hands with salt water to keep the rice from sticking to your hands and shape the rice into whatever shape you want. The most common shape is a sort of rounded triangle.
Repeat these steps with the remaining rice.
Basically, you can add whatever you want to these. Teriyaki chicken in the middle is good, and some people use fish or chicken. If you want, you can also put a strip of nori on your onigiri so it will be easier to hold.