Lightroom 5 is a great piece of software. I use it to manage my entire photo library as well as process my favourite images, occasionally with a little extra work in Photoshop if necessary. Sometimes the changes in post-processing will make only a small difference, such as a slight adjustment to the lighting or removing a blemish. Occasionally the change will be more dramatic, either to better reflect my memory of the original scene or to create a more interesting and, I hope, better photograph.
To give an example of the difference post-processing can make, here's an unprocessed image of our hire car on our recent visit to Norway:
I always shoot in RAW mode rather than JPEG. That was the camera is recording all the information it can rather than performing some initial processing to create a JPEG file. RAW files do take up more storage space, but give you more flexibility in post-processing.
I usually take a few similar images of any given scene, so my initial approach varies. If I know immediately which of the images I like best and want to spend time on, I'll start by looking at the crop to see whether I can improve the composition, then start to work on the colour tones. If, as in this case, I'm not sure whether the image will work, I might make a few other quick adjustments first to see how the image is likely to look if I work on it more carefully.
The initial adjustments I made here were:
Highlights and Shadows - Lowering the highlights is a common technique to restore more detail to the sky. In this case I have dropped the highlights fully and opened up the shadows very slightly.
Crop - I like the width with the wide angle (18mm) but there is too much tarmac between us and the car, so I chose I wider 16:9 crop. I try to stick to the more standard dimensions if possible to make printing easier.
Vignette - I know I want to darken the image significantly, to draw attention onto the car as much as possible. I might choose later to apply separate graduated or radial filters to darken or lighten more specific areas (the old 'dodge and burn' techniques from film days) but for now a heavy vignette gives me a rough idea of how the final image could look.
Those quick changes are enough for me to see that I can get an interesting result from the image, so I start to make finer adjustments and look at the smaller details:
Spot Removal tool - I want to remove the distraction of the pole just to the right of the car and the SR tool can do this by 'painting' along the line of the pole.
Exposure - Raising the overall exposure a little just brings out the reflections on the front of the car more effectively.
Contrast and Clarity - I raise both to give a little more definition.
Filters - I experiment with radial filters to highlight the front of the car but decide that the strong vignette works just as well.
Vibrance - Finally a raise the vibrance to just bring out a little more colour in the sky.
This is the final image:
Hopefully that gives you a useful summary the changes I might make and how powerful Lightroom is as a tool to adjust or enhance an image.
Different photographers view post-processing as anything from an essential component in digital photography to a horrible distortion of reality. It is nothing new though, as modifications in the darkroom were common long before the digital era. Think of it like a good pepper sauce. Too much and you're going to ruin things, but used effectively it just might bring the right amount of spice to enhance the flavour of your work.