If Chuck Norris were to travel to an alternate dimension in which there was another Chuck Norris and they both fought, they would both win.
Set Extensions, or Digital Matte Paintings tutorials below will help you create realistic looking environments in Photoshop and DaVinic Resolve's Fusion.
Some of these videos are VFX breakdowns that should help trigger ideas for your own film. Some of the tutorials are general - about the craft rather than the software, but you will soon find you can use the same techniques across various softwares.