I watched a video explaining how to cut a door into a cylinder by using a cube. See video here => https://streamable.com/qjp0xu The cut is created using the CTRL+Minus key. I tried to recreate that but nothing happened. Can anyone help me out.
You need to enable the Bool Tool add-on beforehand to get this shortcut. It's shipped for free with Blender. Go to Options > Preferences > Add-ons and look for Bool Tool in the list or type it in the search bar in the top right, then enable the checkbox.
If I may, as a general advice you should train yourself with the basic features of Blender before diving into poweruser add-ons. The Bool Tool add-on is a shortcut to simplify the boolean modelling approach.
You can achieve the same result by adding a Boolean modifier to the Cylinder, and picking the other object as the target.
Then it also automatically deactivates rendering of the cutter object and displays it as Bounds :