LWJGL does not help you with generating terrains.
You would need to build the vertex buffer for a (probably) heightmap yourself.
Until a few days ago LWJGL also did not help you with loading image files in order to upload them as textures.
Luckily the latest build of LWJGL 3 now features bindings to the
stb libraries.
Have a look at
this demo showing an example of how to load an image.
Also please understand that LWJGL is not a game engine/library which ought to make game development particularly easy.
LWJGL is merely an "enabling technology" which just enables you to use the very-low-level
OpenGL API as well as some other low-level APIs for sound (OpenAL) and compute (OpenCL).
Nowadays, I probably would not advice people to use LWJGL for game development except for the very very simplest of simple of games, such as two rotating triangles, because very soon you will find yourself in the needs for more higher level stuff, even starting at the very basics such as a linear algebra library, which LWJGL also does not feature.
You probably want to use
libGDX, which has more high-level stuff, such as image loading and camera controls.
Or go big from the start with Unity 5 (does not use Java, though).