Making a model for gmod

I have a model that I want to make playable in Gmod.
So I was wondering where do I start?
How do I rig it, make it into a playermodel etc.
So I’m asking what do i need to do before I can use it
in gmod, i.e a list etc.

This would really help me learn,
any help would be great.

P.S I already have a valve biped but I don’t know how to make it fit my
model and how to make it attached to my model.

You need a modelling program, some tutorials and the smd import/export scripts for which ever program you use.

Best to start with props rather than ragdoll/playermodels if you’ve never done anything like this before.

Edit: Also about the biped, you have to fit the model to it not the otherway round, that way horrific errors lie.