With Lightroom, every single development settings applied to a photo is automatically added to the history, which appears in the left sidedebar of the development module; there is no save action, every adjustment is automatically recorded as metadata without ever changing the original file - that's why it is called non destructive editing. To revert back to the original, you can indeed click on reset, or you can travel back to any point in time in the history, all the way to the import state; note that the reset button will add a reset step in the history and all previous adjustments will remain available in the preceeding steps recorded in the history.
LR doesn't open or save your image files.
On import it builds previews of your files. You apply changes in LR to this preview. These changes are saved in LR's database not in the original file. When you want a version of the file with the LR changes you export and create a totally new file.
Your original file remains untouched and unchanged by LR. If you open the original file in another application the changes made in LR will not be in the file.
This is what is meant by non destructive processing.
The Lightroom Community help system (hit F1 whilst in LR) are considerable and include not only the basic help manual that includes this information but links to many video tutorials, you may wish to try it.
You can monkey around all you like since the edits you see in develop mode are saved to a completely separate metadata file (contained in the LR catalog) and your original image remains untouched. If you open the image outside LR you won't see the changes.
LR initially generates a preview based on the original image and then you work off that preview and the associated metadata. LR updates the preview based on each change you make and write it to the metadata for that image as you go along. You will also see each change you make reflected in the history for that image. It's like the history in PS except unlike PS the full history is there every time you open the image in LR. So if you make changes you don't like you can hit the reset button at the bottom right or just select an earlier state in the history and start over.
If you want check out the introductory videos at lynda.com. You can get a one day free trial (google it) and go through as many as you like.
thanks for the helpful replies. Kinda makes sense...although a different paradigm from other programs where you open and change a file. I thought I would watch a couple of videos today & see what else I can learn. It often seems, however, the fasted way to find something out is to ask on a forum. Thanks again!