This is a pretty simple process. Simply take some water and flick it onto each tortilla as you layer them. Nuke for 30-45 seconds. They come out warm and fluffy.
If you have older ones that are becoming a bit stale but are still good ( not moldy ) use the same method above but cover with a plastic container and nuke for 1 min. this will cause the tortilla to become moisturized again. May possibly need a second nuke if still dry.