After you have created your ingredient rich slab. It is time to roll it up. I like to compare this process to rolling up a sleeping bag for camping or a winter coat for summer storage. On a much smaller scale of course.
Using your fingers to hold the bits inside you will need to turn the front edge over the ingredients (stuff) and then it is time to tighten. After you have rolled up your stuff you will need to utilize the mat. You will notice a bit of extra nori at the top edge of your roll. Dip a finger in ice water and "paint" the nori edge with the water. This will allow it to stick to the roll. Continue to roll the roll until it has rolled over the nori edge. Now you will need to make sure it is sealed.
There is a scene from the movie The Big Lebowski
where Jesus is polishing his bowling ball. This motion will be used by you to tighten and seal your roll. CLICK THE LINK if you are not aware of the motion I am speaking of.
Remove the roll from your mat and set it aside.
Make as many rolls as you have stuff for.