ShadowCaster pass URP

Hello, so I've been learning how to make shaders this past 2 weeks, I started making shaders in the old pipeline and got decent results (I want to make a toon shader, with colorbanding). So I decided to move to URP because I needed the depth texture to add more features to my shader, so I tried to make shaders by code in URP. To be honest, it's a little bit complicated whitout documentation, but I really want to do it by code. I got a simple Lambert light model working, and I just want a base color as an input, but when I started working on the shadow caster pass, I saw that the built in method uses a BaseMap and a cutoff properties. I'm no shader expert and I don't know how this pass works, there's little documentation and I don't want a base map or other properties around there just to make the shadows work. Can someone give me an explanation on how this pass works in URP? How can I make it work using just a base color?
I've been using this guide: https://cyangamedev.wordpress.com/2020/06/05/urp-shader-code/10/

 

For the moment, I made the frag function just return 0. I'm guessing that if I want a transparent object in the future, i'll have to use another method.