Photos comes in many shapes and sizes. Some photos are wide and expansive while others appears tight and compressed. The way a photo is conveyed is heavy reliant on the 'focal length' used for the photo. Focal length is often referred to as how zoomed in you are. This can also be referred to as angle of view. Although focal length is an actual length that is expressed in millimeters (the distance between the optical center of the lens and the film plane). The smaller this number is, the wider your angle of view will be. This works the other way as well where the larger the number, the narrower your angle of view will be.
An important thing to understand is there is two ways to 'zoom.' Using a longer focal length lens is one way, you can also use your feet to zoom though. Moving closer to your subject has the same effect as zooming in (though not identical). Conversely you can walk backwards to zoom out. Now these won't have identical effects. Zooming with focal length will create compression in images where as simply walking will just change perspective. Same with walking backwards to zoom out, this will simply change perspective vs exaggerating your perspective with a wider angle focal length.
Focal length also largely has to do with what type of camera you are shooting on. Crop factor is what I am referring to. This deals directly with your sensor size. The larger your sensor, the larger your angle of view will be. To get the equivalent focal length you multiply the focal length by the crop factor. Most focal lengths are stated in terms of their full frame or 35mm equivalent lengths. 'Crop' Sensor camera usually have a 1.5x crop factor. Meaning if you shot with a 24mm lens on a crop sensor camera it would result in a 24 x 1.5 = 36mm focal length.
When you are discussing focal lengths used, you should be using the number after the crop factor has been applied. So if you shot at 24mm on a crop sensor, you should refer to the image being shot at 36mm. Whereas if you used the same on a full frame it would be 24mm.
Common focal lengths
12mm-24mm: Ultra Wide Angles used to shoot architecture and landscapes, used to emphasize perspective (I shoot most of my images on this focal length range)
24mm-40mm: Wide angle used to shoot things wide, but make them still look natural. A lot of shots are taken in this focal range for day to day shooting.
40mm-70mm: This is a normal range that is pretty similar to what you see with the human eye, a very flexible range. My most common lens I keep on my camera is my 24-70 for how versatile it is.
70mm-150mm: Telephoto lens used for portraits and longer landscape or street shots.
150mm-600mm: Typically used for shooting sports and wildlife
Hope this helped you understand the focal length of your lens and camera. Please let me know if there is anything I didn't address.
Stay true to you.