About Textures in Blender (most recent version) HELP

So I have downloaded a 3d model but it didn’t load in with the textures which is also a frequent problem for me but I usually have to manually add in textures using principled bdsf… Thing is, is that when I click on different material nodes it switches the entire part’s texture to that one node but I want all of the nodes to overlap or combine with each other to make the final result and you would think that would work once you have all the textures but it doesn’t… Why? I have a video here showing what I mean And by the way when exporting it selects that one material or texture selected before exporting too so its not a view thing it actually applies it here’s what I mean: https://youtu.be/2-Ksewx_wEs