However many tortillas your recipe calls for, take that many. Slice them in half so you have a bunch of semi-circle shaped tortillas. Like so:
Now, I take the flat edge of the tortilla and place it against the edge of your 9x13 pan, or whatever you use. It usually takes me about 8-9 half tortillas to cover the bottom. Then, I place the filling in between, and cover the top with the remaining half of the half tortillas, cover with enchilada sauce and cheese, and Voila! You just cut it up like lasagna and serve it!