Here is how i make terrain with texturemaker.

It is not step by step, because every situation is different. i suggest taking a day or two, and make some brick wall textrues or something non-mapping so you get the hang of TM.

First off i use the heightmap tools to create a bumpmap for my terrain.
EVERY tool is capable of making bumpmaps, look in the presets.
I focus mainly on the Perlin noise tools: Heightmap mountain, and heightmap river.

Teh mountain tool lets you draw globs on the map that have an eroded earthy look to them. You use the circle tool for this, so you can drag out an elipse, and it poops down a mountain for you. You can set the elevation by the shades of grey that you use.
For Forks, I used a maximim grey value of 60 and a minimum of 16 grey valye. (All greys are 3 bits of RGB that are exactly the same, 60,60,60 and 16,16,16 are listed here.)

I think the heightmap importer makes an elevation climb every 5 shades of grey.

For other cool patterns look at the perlin noise functions, and use the elipse tool.

To make stairs, just make gradients the same 2 colors you are trying to match. so if you have a wall 96 tall, and you wanted to get to a floor that is 32 tall, just set your gradient tool to 96 grey for the top and 32 for the bottom. If there are missing stairs, means you do not have a long enough run. If the stairs are really long, you have the gradient set too long.
Check out :
Errode to make valleys wider
Smooth (atleast 2 times to make everything walkable, and no cliffs)
Gravemetric to make spherical patterns from noise (nice for boulders and gravel)

After i get the heightmap looking all real looking, i pop it into the advanced mixer:
http://img98.imageshack.us/img98/2784/tm2ez.jpg

As you can see from the photo, there is a grey gradient on the mixer tool, next to a gradient of all the color sliders. i set the sliders to the level I want the color in the greyscale heightmap.
As you can see i have some colors overlapping. This gives a nice fading effect for the transition from sand to dirt, dirt to grass, etc...

I even have it set so anything over 64 grey (64,64,64) is a grey like cement. This is for roads, sidewalks, building foundations and whatever else.. I have 3 diffrent shades, so I can do Foundation, walkway, and road. (later it is really easy to flood fill in other colors if you need more than 3.)

Then I pop it into the advanced shader editor. The Shader editor is made for testiung yout your bumpmaps and textures that you will be later using in other 3d applications.
It is really AWESOME for doing terrain shadows, and definition too!
http://img263.imageshack.us/img263/5356/72145783.jpg

There is an omni light source (ambient) so that you can set it to fake AO, and not have any areas totally burned black.

Other nice things to tweak:
Turn both shine sliders off (unless you want slime or snot specular reflections).
Amplification sets how tall things are. great for tweaking shadows.
Shadow length... really easy to over do this one, but can also make your map look really moody.
Smoothness... If you are getting pixelated, or sharp corners use this to tweak them.

Well as you can see it does the hardest thing... GETTING THE WATER AND SAND LEVEL RIGHT!
After you set it once, you will never have to tweak it again.

So that is it, the most time consuming part is actually laying it out, and drawing the heightmap.

If you want to make housepads on your heightmap, just make your rectangles or whatever, at the elevation you want, and smooth it into the terrain.

One last note
TURN OFF BLUR,SUPERSAMPLE, AND AA for any tool you use. it will not make crisp edges if you do not.

Have fun!

I will release a prefab pack soon here so new mappers can just go into the randomly generated maps that AOS makes, and press F1... then they can just go to voxxed, point, press U , and place little houses and trees and stuff.

Terrain maps are the easiest to make because you do not have to explain what , and why things are there.... Rather than having to map out a house for a strategic obsical, you just add a blob for a hill.

Also try not to have too many hills and valleys around. Flat ground is best for walking. falling and climbing all the time makes getting around really lame. I try to smooth things out to make every surface walkable, with long flat ares for paths.

Anyway, have fun!