Lava Door is used to counter the mobs . You can pull the lever down whenever a mob enters the door and lava will start flowing in the room.
This guide will explain to you the method to make a Lava Door in the Minecraft game.
Oak signs will help to keep the lava inside the wall. The next thing you need to do is to dig the ground in the middle of walls and place smooth quartz blocks there. Place dispensers at the top of walls and add a lava bucket in each of them.
Add smooth quartz blocks on either side of dispensers. Fill the side gap with smooth quartz blocks as shown in the following image. And then use redstone dust at the top of these quartz blocks.
Add a stone button on two opposite sides and your Lava door is completed now. Press the button to start the flow of lava and press it again to stop it.