Can you describe what you are trying to do and what you feel it is that makes your efforts appear unrealistic?
As you said, the terrain tools are fairly easy, just remember that each tool has settings available by right clicking on the tool button
As examples, the level tool has settings for clamp, height and radius, where the raise and lower tools have settings for radius and strength... By playing with these tools and their settings, you should be able to manipulate base terrain to your standards with some practice
Beyond that, spending some time learning how the various textures work together and adding placeables should get you where you need to be
If you can't get something specific to work, post questions with all the details you can think of
