Simple cases first ...
Apply one of the text generators (like Title3D or Lower Third) to your video clip. Enter your text. It will appear as part of the video in your clip. You will have some limited capability to position the text within the video frame.
Another way, apply a text generator to a video track above the one your video is in. (If your video is on V1, then put a text clip in V2) You can then manipulate the resulting text clip and composite it with your video in track V1. You have some greater ability to manipulate the positioning & shape of the text this way, by using the controls in the canvas in addition to the controls in the text generator.
If your wall example is what you really want to do, and the wall is stationary in the video frame, then the above will probably suffice. If the wall moves (eg due to camera movement or panning), then you will probably have to use motion keyframes to move the text in alignment with the movement of the wall in the video frame; this will take some trial & experimenting.
