Here you can find the basics, including where to download Prelewd, how to use it, etc.
What is Prelewd?
Prelewd is a 3D porn simulator with VR capabilities and support for SFM animations, Source Engine (and Source2) assets, as well as VR/360 videos. It currently has limited interactivity options (such as replacing characters, changing skins, bodygroups, sets, etc.) and has both a VR and a non-VR mode (i.e. you don't necessarily need a VR headset). Using the animation retargeting system, you can replace the actors in the scenes with any Source Engine character you want (e.g. from https://sfmlab.com/), even if the model has different proportions or a vastly different skeleton: