Using the RS winder

Step by step instructions (or just watch a video):

1. Prepare all the parts needed: the winding barrel, the winding base, the plunger, the setting bowl, a staple cut into the shape of a hook, and the mainspring (Seiko NH35 in the example below). The square plastic piece is the staple jig for cutting the staple to size, however you may not really need it if you can comfortably eyeball the correct size:
   

2. Place the mainspring into the arbor rod on the winder base, or go from the inside out as recommended by user Yxoc from WRT (link). Use tweezers to latch the arbor hook into the mainspring hole, make sure to follow the recommended style:
   

3. Carefully put the housing barrel and winder parts together. Take care not to wind in reverse as this will unlatch the anchor:
   

4. With the barrel and base held together, use slight finger pressure on the plunger. This helps keep the spring in a flat plane, as it feeds into the barrel and prevents it from getting tangled:
   

5. Wind the mainspring until the bridle approaches the winding aperture. Gently feed the initial bit in by hand, and then wind the remainder into the barrel:
   

6. Once done, carefully allow the base to unwind in the reverse direction until there is no more backpressure from the mainspring. The anchor should naturally unlatch, allowing you to easily take off the winder base part:
   

7. Carefully remove the staple with tweezers before placing the barrel into the setting bowl and pushing down with the plunger. The wound spring will be extruded out of the barrel by about 1/3 mm:
   

8. Carefully fit the actual mainspring barrel into the extruded portion of the mainspring. Place the parts on a level surface, you may flip the setter bowl part and use it for this purpose. Then plunge it home!