When you “show someone to the door”, what you are doing is seeing him off at the door.
Here are a few examples. *Uma always makes it a point to show her guest to the door. *After the meeting, Raju showed me to the door. *I told Sandeep that he didn’t have to see me to the door.
When you show someone the door, you are forcing the individual to leave. You are asking the person to get out. *When the students misbehaved, the teacher didn’t hesitate to show them the door. *The gatecrashers were shown the door in no uncertain terms. *If you don’t behave Reema, I’ll have to show you the door.