I am trying to wrap a car model in Blender 2.9. I am new to blender but have used other 3D modeling programs and rendering programs. I have applied the image texture to my material, and I believe I have done it properly. It shows up when I am in solid mode and have texture enabled, but does not show up when I switch to material preview. below are pertinent screenshots. The way that the texture shows up in solid mode is EXACTLY the way I want it to look in material preview and rendered.EDIT I have plugged the texture into color instead of roughness, but now it shows up as just a solid color (see last image). scale is set to 1, 1, 1. the image is the correct size according to the UV mapping, so it should not need to be scaled.
As @scurest said in the comments, you need to reconnect the image texture node to the color input of the principled BSDF shader, instead of the roughness.
Currently, your image is controlling the roughness of the area it is unwrapped to, based off of the colors in the image. If you want this effect still, then simply leave it connected to roughness, and connect it to color. Therefore it will determine both color and roughness of the area it is unwrapped to.