My family used to live in Japan, so my mother made sushi rolls, rice presses, and onigiri a lot when we were younger. I learned from her, and I won’t pretend that these are 100% authentic or visually appealing, but it’s how I’ve always made them.
Start with a bamboo mat–you can buy them at most Asian food stores–and lay it out on your counter. Since the outside of my roll is seaweed I didn’t wet my mat, but if you’re making a roll with rice on the outside you definitely need to brush the mat with water. I lay a sheet of seaweed on the mat, then spooned sticky rice on. My rice was made about two hours prior, doused in a generous amount of rice vinegar, and mixed with some furikake (often known in the US as rice sprinkles). The vinegar loosens up the rice a bit and adds a sweet flavor. Spoon it onto the lower third of your seaweed sheet. If your adding sashimi or vegetables, I find it easiest to put them on top of my rice, then add rice on top as well. This just promises you a filling in the center.
Now lift the bottom of the bamboo mat and curl it forward–your hope is that the bottom edge of your rice will circle over to meet the top edge of your rice. When this happens, continue to roll your rice tube forward squeezing slightly with the bamboo mat. Brush some water on the edge of the seaweed to seal your roll when you finish.
Before you cut your roll, pour a glass of water tall enough to stick your knife into. You want a very sharp knife, and it has to be wet so that the rice doesn’t cling to it. Enjoy your sushi roll!