Lightroom is a non-destructive editor. This may be different than anything you have used in the past.
With non-destructive editors, there is no concept of original and derivative (unless you choose to use a 2nd program like Photoshop, sounds like you're not planning to do that). With a non-destructive editor, you make your changes in the editor (Develop Module), and these instructions are stored by Lightroom as a "recipe" and not as a distinct file on your hard disk. These instructions about your edits are applied whenever you use Lightroom to view your image (or whenever you choose to print from Lightroom or make a slidesehow from LR or make a web page from LR). The original is completely unchanged, and there is no edited derivative photo exported or saved. Thus, there is no need to segregate original and edited photo, because there is no saved edited photo. Additional edits in Lightroom are handled the same, original is unchanged, your edits are stored, and there is no derivative or saved photo.
The only time you would save a copy of the photo is if you wanted a copy for some non-Lightroom purpose, in which case you use File->Export... to make a file on disk in a "temporary" folder, then you use the file created in whatever non-Lightroom purpose you have, and when completed, you can delete the file in the temporary folder, knowing that LR can re-create it exactly if you ever need it again. If you are going to print from LR, or e-mail from LR, or create a web page from LR, or create a slideshow from LR, you do not need to create an exported photo.
JPGs and RAWs and DNGs are all handled the same by you, the user. Yes, there is internal differences that aren't important to your workflow.