Basic Usage of .MTL in OpenGL - c++

Question

I am currently parsing the .mtl file associated to the .obj file I have. I can properly render the model, but how can I use the .mtl file? Where am I supposed to send the values of it? How do I use it? Currently, can't find anything that uses .mtl file in OpenGL. They just show how they parse it.
EDIT :
This is how do it in OpenGL. I have also created my own OBJ parser. Notice that the code is shorten for just an idea for you how I am doing it.
GLuint vao;
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
GLuint buffer;
glGenBuffers(1, &buffer);
glBindBuffer(GL_ARRAY_BUFFER, buffer);
glBufferData(GL_ARRAY_BUFFER, cc * sizeof(GLfloat), v, GL_STATIC_DRAW);
GLuint tcbuffer;
glGenBuffers(1, &tcbuffer);
glBindBuffer(GL_ARRAY_BUFFER, tcbuffer);
glBufferData(GL_ARRAY_BUFFER, tcc * sizeof(GLfloat), vt, GL_STATIC_DRAW);
GLuint ncbuffer;
glGenBuffers(1, &ncbuffer);
glBindBuffer(GL_ARRAY_BUFFER, ncbuffer);
glBufferData(GL_ARRAY_BUFFER, ncc * sizeof(GLfloat), vn, GL_STATIC_DRAW);
glEnableVertexAttribArray(m_vert);
glBindBuffer(GL_ARRAY_BUFFER, vbufferid);
glVertexAttribPointer(m_vert, 3, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(m_texcoord);
glBindBuffer(GL_ARRAY_BUFFER, tcbufferid);
glVertexAttribPointer(m_texcoord, 2, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(m_color);
glBindBuffer(GL_ARRAY_BUFFER, cbufferid);
glVertexAttribPointer(m_color, 4, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(m_vertexnormal);
glBindBuffer(GL_ARRAY_BUFFER, ncbufferid);
glVertexAttribPointer(m_vertexnormal, 3, GL_FLOAT, GL_FALSE, 0, 0);
glDrawArrays(GL_TRIANGLES, 0, vc);

Answer 1

The MTL file accompanying the .OBJ file is a description of the materials applied to the .OBJ mesh.
For each material, it specifies the texture path and several color properties like diffuse and specular color.
OpenGL doesnt care about .obj, so it also doesnt care about .MTL, the way you use the data is up to you. There's a couple of ways to apply the data in the .MTL file to the opengl mesh.
The easiest way to do this is as follows:
Look at the OBJ file's USEMTL instructions and seperate the faces based on material, basically, whenever you see USEMTL X, all following faces are to be drawn with material X until you encounter a new USEMTL Y.
Then when you draw, for each material called MAT: bind the texture from the .MTL file for MAT, set the diffuse and specular parameters for MAT, and draw only those faces where the .OBJ said USEMTL MAT.
There's a few other ways to be a lot more efficient about it, let me know in the comments how you currently draw your mesh, since this has some influence on what the best option is.
The MTL file can contain some more advanced stuff but this should get you started.
For more info on the MTL file and what the values mean, see Wavefront .obj file.