What the Door for?

I haven’t seen and instructions on how to use the oven door that comes with the kit, we’ve yet to have our oven heat up correctly enough to make a perfect pizza, (but were close) I tried to use the oven door that comes with the kit to heat up the oven more… well it worked and now I have a crack that goes completely rounded my oven. I’m still thinking of a door. without the door I use a lot of wood and I don’t have enough heat on the cooking surface.