I'll jump right and welcome you to the science of watchbreaking !!
This is a simple approach to your question, and others will have more to add I'm sure.
Yes, the outer ring does come off. Be careful not to tweak it. The "dimples" help to hold it in place.
Once it's removed, (even before, if it will fit with the ring still on ) you want to get that movement into a holder.
You never want to disassemble a watch with a wound mainspring. You can literally destroy many components.
The small item you are seeing in the "window" of the plates, right below the mainspring barrel, should be the detent that you can press to relieve the spring.
So here we go...
1. Put the movement into a holder
2. Replace the winding stem/ crown into the keyworks, and slightly tension it as though you were going to wind it further.
3. While holding that tension, you want to press against the detent with say a piece of pegwood,and once it starts to release you want to make sure that you let it down slowly,..by keeping tension on the crown, and letting it "slip" slowly in your grasp until it is "at rest".
Best of luck...