Hey @eireen , that question means you’re ready for the next step! You could apply materials and such to these models, but I’d actually recommend moving on to other projects for learning that. Here are a few courses that will show you how to make just about any kind of material or texture:
https://cgcookie.com/course/shading-fundamentals-in-blender-render
https://cgcookie.com/course/shading-the-sci-fi-helmet
https://cgcookie.com/course/the-blender-substance-texturing-workflow
https://cgcookie.com/course/texturing-weapons-in-blender-and-substance-painter
https://cgcookie.com/course/shader-forge
https://cgcookie.com/course/creating-mini-tanks-for-a-mobile-game
Each of the courses show a slightly different method – try them all and see which you like best! Happy rendering!