Creating new shader uniforms for OpenGL ES 2.0

Hi is it currently possible to create a new shader uniform for OpenGL ES 2.0 .
I looked into the code but I can’t understand how it works.
For example for the depthBuffer and the normalBuffer I found only these:

engine->RegisterEnumValue("TextureUnit", "TU_NORMALBUFFER", TU_NORMALBUFFER); engine->RegisterEnumValue("TextureUnit", "TU_DEPTHBUFFER", TU_DEPTHBUFFER);

textureUnits_["NormalBuffer"] = TU_NORMALBUFFER; textureUnits_["DepthBuffer"] = TU_DEPTHBUFFER;

Where are the OpenGL calls for these guys ?
How are these translated to these samplers :

uniform sampler2D sNormalBuffer; uniform sampler2D sDepthBuffer;

Thanks in advance,
Alex