It really depends. I personally don't rinse it before use, but others recommend that it's rinsed. In my experience, if it's rinsed before use it starts to become muddy and is difficult to work with.
Typically you would place stratum in your tank, place your decor add a little bit of water so you can start to add some live plants, then fill the rest of the tank. That said when you fill your tank be sure to protect the stratum with either a plate or a plastic bag.