dynamic 3d fog in raycast

I am currently making a doom-like 3d ray casting game. I would like dynamic fog in it, but I have no idea where to start or how to display it. Any ideas?

@That747guy I have some code for fog If you want I can send it to you

@Waylonbb I would appreciate it. Thanks, man.

any time and here's a link to the code: https://docs.google.com/document/d/16s0F8oziEvSmcDHF3eOEVChMW9S0vKgWyRqBwI4RuVI/edit?usp=sharing

Btw I really like cowboy showdown it's pretty fun.