'Sushi grade' fish is just fish that has been frozen, which kills of any potential parasites that might otherwise be an issue when eating raw fish. I make sushi using (defrosted) frozen salmon fillets (just from the supermarket, nowhere fancy).
Make your rice following the instructions on the packet, mix with sushi vinegar, leave to cool.
Place your nori, shiny side down - you might see lines across the nori sheets - place your sheet so these lines run horizontally. Spoon some rice on (less than you might think) and smooth out. Leave about half an inch of nori free of rice on the edge closest to you, and leave the top third of the nori free of rice too.
Then add your fillings! I like salmon sliced thin, avocado, grated carrot, blanched green beans and asparagus, sugar snap peas, spring onions chopped fine, cucumber. Strips of omelette are nice too (make a really thing one in a smallish pan with only one or two eggs).
If you don't want to use raw fish, try smoked salmon. 'Teryaki' tuna is nice too - mix tinned tuna with soy sauce and mirin.
Roll from the side nearest to you, folding the rice-free edge over first. I find it easier without those bamboo mats. Roll it up, nice and tight, then dip your finger into a some water and run it along the far edge of the nori before you finish rolling - this helps seal it. Cut with a sharp knife - if it sticks, run it under cold water.
Enjoy!