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What type of laptop are you connecting to the Tv
The process of using the windows key and P would be for using a physical cable (HDMI cable) plugged into the TV and laptop to get content displayed.
If you want to do it wireless you would need to use some form of streaming app on the TV and laptop, the best way to do this is use Chrome Cast which can be found here, this is a piece of hardware which plugs into the TV HDMI port at one end and an app on your laptop or phone which then connects to the chrome cast. The way this works is explained on the video here.
Let me know if you have any further questions.