In this tutorial i will show you how you can make rocks in HAmmer editor. It's only one of many ways to create rocks. You require a foreknowledge with the vertex tool. I have marked the screenshots with numbers.
Select a good rock texture you want to use...
At First create a line of brushes with the same high but different lengths. Like screenshot 1. You can decide for yourself how many brushes you want to use. I take 4 brushes.
Now take the vertex tool and select 2 edges of the brush and drag them to the front... Its the best you look to screenshot 2.
Now select the brushes and hold SHIFT and clone them directly above the first brush-line. Like screenshot 3. This will set the height of the whole rock
Now take the vertex tool again and select the top edges of the top brush-line and drag them to the back. I marked them in screenshot 4.
Then do the same with the lowest brushes but in the other way. Like screenshot 5
Take the clipping tool and clip some of the uppest brushes like screenshot 6 (in 5)
Finish! questions? Ask!