If you are using 3D engines like Unity, it will be pretty easy.
And if not, generally you need to (if you are using OpenGL ES 2.0, like the samples)
- load the image into memory
- upload it to GPU through gl callings
- render the texture using gl callings and shaders
You may need to learn some OpenGL ES 2.0 basics if you are not familiar with that, and you will find it very easy when you know how to render a texture into 3D space.