Rinse the sushi rice in cold water until the water runs clear. Drain the rice and transfer it to a saucepan with 4 cups of water. Let it soak for 30 minutes. After soaking, bring the rice and water to a boil over medium heat. Reduce the heat to low, cover, and simmer for about 15 minutes or until the rice is cooked and the water is absorbed.
In the meantime, prepare the sushi vinegar mixture. In a small bowl, combine the rice vinegar, sugar, and salt. Microwave the mixture for about 30 seconds or until the sugar and salt dissolve completely. Set it aside to cool. Once the rice is cooked, transfer it to a large bowl and let it cool for a few minutes. While the rice is still warm, gently fold in the sushi vinegar mixture, ensuring that every grain of rice is coated. Be careful not to mash the rice.
Now it's time to assemble the sushi rolls. Lay a sheet of nori on a bamboo sushi mat or a clean kitchen towel. Moisten your hands with water to prevent the rice from sticking, then take a handful of sushi rice and spread it evenly over the nori, leaving a small border at the top.
Place your desired fillings (such as sliced cucumber, avocado, crab sticks, or any other ingredients) in a line across the middle of the rice.
Using the sushi mat or towel, start rolling the nori tightly over the fillings, using gentle pressure to shape it into a roll. Moisten the top border of the nori with water to seal the roll. Repeat the process with the remaining nori sheets and fillings until all the sushi rolls are assembled. Use a sharp knife to slice each sushi roll into bite-sized pieces. Dip the knife in water between each slice to prevent sticking.
Serve the sushi rolls with soy sauce for dipping. You can also accompany them with pickled ginger and wasabi for added flavor.