After your canning time is done, turn off the heat, remove the lid from your canner, and carefully lift each jar out using your jar lifter.
Place the jars onto a dish towel on your counter. Leave about 2 inches of space between the jars to allow air to circulate and cool them off. Don't retighten the bands until the jars have cooled 12-24 hours.
It's really amazing when the sealing compound sets the lids. You'll hear them "pop!"
After your jars have cooled, check the lids for a good seal by pressing down on the lids. They should not flex if there's a good seal. Double-check by removing the bands and gently use your fingertip to try to remove the lid. If it doesn't flex and you can't lift the lid, then it has a good seal. Replace the band and label the lid. You can use a fancy label you print from your computer, or simply use a sharpie marker and write on the lid. The lids cannot be reused, so it won't hurt anything to write on the lid.
I can't wait until the morning comes to see if all my lids have set correctly. We learned that we could have packed the jars a little better with tomatoes (see picture above, all the tomatoes floated up towards the top). Oh well, you live, you learn. I think we did a good enough job for our first tomato canning experience. :)