Beginner

This person describes the whole process he did to make a fantasy landscape.  He blocked out the shapes for his idea, and then added some elements like a picture of a hiker, some landscapes, and textures them, and then lights, and adjusted his camera.    He then goes over all the steps he did in photoshop which were straight forward.  I'm sure you could use gimp or something like that also.  Overall a very nice tutorial.  The addition of photoshop really makes the image much nicer. He shows how to use layers or color grading, color, fog, shadow to make the image better.

Intermediate

Advanced

Timelapse of a very nice sci fi scene.   He composes stuff with kit bashing items, and lo poly stand ins.  Then replaces with high res models for somethings.  In photoshop he adds in some fog to separate objects from the background and add depth.