_BlitTexture ? Input textures from a render pass, renderer features

Hello, when making a shader that is injected into the renderer graph with a renderer feature,

I followed the docs example (at the bottom of the page is the shader code ):

I would like to know where does this texture “_BlitTexture” come from I kind of am confused about the input situation , I totally understand the C# part but how they are obtained in the shader confuses me, as in what if we have two or 3 inputs <— this is my main question and also the “input.texcoord” part what else is in the input var?