It's my understanding that opening them as smart objects doesn't have anything to do with non-destructive editing. It simply allows you to do things like using smart filters with them.
Here are the basics of non-destructive editing:
1) Start off by duplicating your background layer and never touching it again; that way you can always go right back and start from scratch.
2) Use Adjustment Layers rather than doing tone and colour changes on the image itself.
3) Do any pixel editing, such as brush work, either on a duplicate layer or select the part of the image you want to edit and press Ctrl+J to bring just that part onto a new layer on its own, then work on that. Examples would be touching up skin or lightening and sharpening eyes.
4) Do cloning/healing on a separate blank layer with the clone/healing brush set to 'Sample all layers'.
5) Do dodging and burning on a layer filled with 50% grey and set to Soft Light blend mode; then use a white brush to dodge and a black one to burn, set to about 10-20% opacity.
There's probably a lot more I've left out but it's late and my brain hurts

. Anyway, you'll pick it all up in time. If you need to know more, just ask.