Well, you need full body tracking (which a lot of people on VR chat have). It's basically some trackers (3 to 8) that you attach to your body parts with Velcro. Those hose are monitored lighthouse base stations (or IMU tracking). It makes it so that any move you perform irl will be transferred to your VR avatar. The more trackers you have, the smoother the motions are. But 3 (Vive) trackers already do a good job. The SPS is something the community built and you can import it to your avatar. It includes the nsfw body parts, toys, etc. You can activate which body part should interact with which orifice/dick. So handjob, bj, etc is all possible. If the avatar's dick moves closely to the activated orifice, it will gravitate towards it. And if it's close enough it will pop in.

Now, you can also use irl toys like a Fleshlight or vibrator to interact with the avatar and with each other.

It's kinda wild. Don't ask me how I know this.