There's certainly tens of different ways to make onigiri, the Japanse rice balls consumed as snacks or incorporated into meals. If you've had that kind of sushi that is not rolled up (makisushi), but which instead consists of an elongated ball of rice with something on top, you are no stranger to nigiri - you've had nigiri sushi.
To me, onigiri is like comfort food: the delicious chewiness of rice, slightly salty on the outside, blander on the inside until you stumble on some kind of filling, possibly. Today, I made this version on the left with my 8 year old dude, at home.
Simple cooking: we made a couple of cups of sushi grade rice in a rice cooker (no salt or other seasoning) and left it to cool down a few minutes. Then we shaped the rice balls with triangular molds, which I picked up at Liberdade, the Japanese neighborhood in São Paulo. You can use your bare hands, if you don't have a mold.
We prepared a bowl of salty, cold water for us to dip the molds in (if using hands, guess what, we'd have dipped our hands in it). We filled half the mold with rice, put a few pieces of umeboshi on top and filled with more rice. Then we pressed the lid of the mold on the top just to firm up the rice ball (we wouldn't want to hard pack the rice into a heavy brick!) Out of the mold it comes for a sprinkling of furikake, which have found at Wegman's and at oriental food stores in Calgary, AL, Washington D.C., and Gaithersburg, MD, among other places. Furikake comes in different flavors, so you can get creative with your choice. Before making another onigiri, dip the mold or your hands in salty water again.
You can find several other tutorials online for variations on the theme, here is one of them.