It is not that difficult to make sushi, as long as you have all the ingredients and “tools” (such as makisu, a bamboo-rolling mat), which might not be that easy to get outside Japan. From the ingredients, you need nori (seaweed), cooked rice (preferably soft and sticky and not salty), and whatever you want to put in the middle (crab meat, tuna, other kinds of fish, avocado, cucumber, etc). After placing a sheet of nori over the makisu, spread rice over it (thinly, so that you can see through it), place your desired filling in the middle in a strip and roll the sushi using the makisu. Press firmly in the end for the sushi to form.
You can find plenty of different recipes for different kinds of sushi, try some of the links below.

1. 1. How to Make Sushicopy
2. 2. How To Make Sushicopy
3. 3. The beginner's guide to making Sushicopy