Textures don't show! Everything is grey

I'm new to the unity engine so please forgive my naivety but I have a problem where my textures do not show at all! If I were to import a model from Sketchup or anywhere else as either an fbx file or obj, the model is imported to unity but its completely without any rendering, so basically it is all grey. I know you can manually drag and drop textures but that too doesn't work :( If I try to drag a texture it ends up looking like this:

so am I doing something wrong here? Do I have to check/uncheck feature ? Thanks for your help!