We have many methods of separating the background image in Photoshop, to isolate an image we just need to use tools that have selection function in Photoshop such as Pentool, Selection tool group. However, these tools should only be used to isolate the background for simple (smooth) subjects such as people, cars, … for complex subjects such as furry animals. Dogs, cats, trees … you should not use these tools because it is very time consuming. Instead we can use the Channel to simply separate the background and get the most details.
The tutorial below by photoshoptrainingchannel will show you how to isolate a subject with more complex details using the Channel function in Photoshop.
Also, you can refer to instructions for separating a simple photo background through the video below: