Best thing for a propane forge is to find a nearby blacksmith that has built one (likely not too hard) and copy his design or get the basic idea. Hands-on is better than a wall of online text for this stuff. Simple solid fuel forges are super easy to make, just a pan big enough with a grate of drilled holes on the bottom center, with an air blast piped in from some kind of fan or blower. The air supply should be adjustable. This can be a choke flap over the fan intake, a dimmer switch in some cases, a big gate valve, whatever.
Oh, and if you've been told this before, it's for a good reason- filling out your profile will help people to help you. You may find someone nearby, willing to help, that posts here.