The next important lesson to learn about photography is the importance of understanding the foreground, midground, and background.  The proper usage of this can create feelings of depth in your two-dimensional photograph.  

The overall concept is pretty straight forward, foreground in the closest part to the camera, midground in the middle, and background is in the very back of your photograph.

In the image above, you can see a clear foreground, midground, and background.  The foliage in front of the deer, in the foreground, pulls us into the photograph but does not distract us from the main subject, which is the deer.  This is because it is blurred and not in focus. The subject of the photograph is in clear focus in the midground. Behind the subject is an out-of-focus background, leaving only the subject in focus and not distracting away from it.  With the use of foreground, midground, and background, this image shows a lot of depth, bringing the photograph to life.

In the image above, we have another example of foreground, midground, and background, except this time, the subject is in the foreground.  The main focus of this photograph is the hands on the guitar. They are in the foreground and completely in focus. As our eyes travel, his arm leads us into the middle ground, along with the rest of his body.  In the background is the black stage, keeping the subject the main focus, but allowing for depth in the image. 

Lastly, the above is an example, using a landscape.  In the foreground, there is green grass and foliage, not quite in focus, but enough to invite the viewer in.  The water against the shoreline is seen in the midground, which is the subject of this photograph. In the background, mountains and more water and greenery are seen, but out of focus.  All of this together adds a lot of depth to the image.

The understanding of foreground, midground, and background can not only help your photography, but also art and cinematography.  They are very important compositional elements that can help in raising the quality of your work.

Sources:

The Concept of Foreground, Middleground and Background in Landscape Photography

https://www.youtube.com/watch?v=V0S5vZKR--Y&ab_channel=MarySwanson