Trapdoors can do the following:  Prevent falls. Prevent mob access to an area. Stop water, snowfall, rain or lava from flowing into an area. Act as an opening for a countertop, such as a bar. It still lets light come through and does not block redstone signals. This is the only way to place a trapdoor. Then you can build around it with other blocks. Right click on it. It will flip back onto the block it is attached to.

How would you rephrase that briefly using Chinese?
活版门可以放在建筑物里。 要放置活版门，放在固定方块的一边。 打开活版门。