How do I undo mirroring

I went to retrieve my phone this morning. Now after a few flips and turns I finally got it upright. When I finally got to working on it, I realized the screen was grayed out. After chatting with Siri for a while I discovered it was screen mirroring. I’m Having difficulty with the instructions Siri gave me. Could you please describe the steps to undo Screen mirroring in detail? Thank you for your time!