I've decided to do a tutorial for FC2 map editing. This is to showcase the power of the Far Cry 2 map editor, and speed up your learning.
Basic Terrains:
As an example, if you want to make a basic mountain, use the NOISE TOOL, which is located on the tool bar, and looks like the following:

.
After you have selected the tool, you need to configure the tool.
The parameters i use are the following:

You, of course, can modify those parameters to get the mountain look like what you want to.
Okay, and now how to use the tool.
First off, hold your left mouse button down, and drag up & down, until your mountain gets some shape. You can keep dragging it as long as you want to, to get the perfect result.
After using the tool & dragging around the map, i got a terrain that looks like the following:

Also, this technigue is ideal for sand dunes, too.
Now, let's get more natural shaping. Use the SMOOTH TOOL, which looks like:

Change the parameters yourself, this time, to get the results you want to.
After a while of smoothing, i got this result:

Then, lets add our terrain some erosion! The tool icon looks like the following:

I recommend you to use these following parameters for the tool:

After a while of using the erosion, i got a lot more natural shapes. As an example, the following:

Looks a lot more natural than just a plain, smooth mountain.
Now, if you like to, you may use the smooth tool on the mountains again, with lower Strength param than the last time.
Sometimes, mountains like this don't look very good. In that case, you might want to add some rocks to the mountains. Remember to use rocks that fit for the map's texturing!
That was for the basic terrain tutorial.