Start with your opponent in your closed guard. This is, by far, the lowest risk option you have available, and therefore a fantastic attack to begin working with so that you can better understand the nature of the wristlock as a submission. After all, if you screw everything up, you've still got closed guard (unless you really, really screw up). Assuming your partner has both hands on your midsection (and this is extremely likely, given proper posture in the closed guard), reach up with your right hand and find your partner's funny bone, right behind their elbow, but shy of their triceps. Use your middle and index finger ("Spider-man grips") to start opening your partner's elbow, and then reach up with your left hand right on top of your right hand, reinforcing the grip. Pinch your elbows together to facilitate the trap, and then pull inward as you sit up outwards, crunching your ribs toward your partner's elbow. The general concept here is to bring your partner's knuckles to their forearm. It's worth noting that the wrist takes a great deal less pressure to break than the elbow or shoulder, so be careful!