As mentioned, Lightroom never changes the pixels of your photograph files.
When you're editing a photograph, Lightroom continually stores the editing instructions in the metadata file of the photograph.
When you export the photograph, Lightroom renders the exported version of the photograph.
The pixels in the exported version are changed.
The pixels of the original photograph are not changed.
Keep it simple, at first.
Mathew Carey Lea (1823-1897) made the suggestion in 1868, and it still applies today.
Scattered editing isn't as good as editing done step-by-step.
Start with the Typical Workflow, and adapt it to your needs.
Generally, you do global edits first.
Global edits affect the entire photograph, such as exposure and color.
Then, you do local edits, such as burning and dodging.
Then, you return to two global edits, noise reduction and sharpening.
Typically, you set the white balance first.
Then, you adjust the exposure.
Adjusting the exposure can change the color.
So, cycle back and have a look at the color after adjusting the exposure.
The next section covers the order that you use the panels and their tools.
We have poor memories for exposure, contrast, and color differences.
Therefore, it's essential to compare before-and-after views of the photograph after you've made a change.
Use the following three methods.
Method #1 is the best one.
You can use keyboard commands to undo and redo your editing.
As mentioned, this is the best comparison method.
You can toggle between your previous edit and the current edit.
To undo the last edit, press Ctrl + z.
To redo the last edit, press Ctrl + y.
To undo the last edit, press Cmd + z.
To redo the last edit, press Cmd + Shift + y.
There's a turn-off icon on most of the tools and panels.
Click the icon to toggle between turning off—and turning on—the editing that you did with a tool or panel.
Unfortunately—when you turn off a panel—all of your editing done with the panel is turned off—not just the last edit.
If you're using the Six Tools panel . . .
. . . look for the tiny turn-off icon in the lower-left corner of the tool that you're using.
The Crop tool doesn't have a turn-off icon.
The Basic panel doesn't have a turn-off icon, either.
The other panels do, on the left side of their tabs.
Press y to see your original photograph next to your edited photograph.
Press y again to see just your edited photograph.
Press \ to see your original photograph.
Press \ again to see your edited photograph.
You've added a powerful feedback loop to your endeavors behind the camera.
By editing, you become a better photographer.
Let's look at the order your should use the panels and tools.