I am a beginner on OpenGL. I have a bit confused on modelview matrix and projection matrix. As my understanding, modelview matrix represents the direction the camera looking at while projection matrix represents the range of clipped space. Is that right?

ModelView matrix is the concatenation of Model matrix and View Matrix. View Matrix defines the position(location and orientation) of the camera, while model matrix defines the frame’s position of the primitives you are going to draw.
Projection matrix defines the characteristics of your camera, such as clip planes, field of view, projection method etc.

The reason for two separate matrices, instead of one, is that lighting is applied after the modelview view matrix (i.e. on eye coordinates) and before the projection matrix. Otherwise, the matrices could be combined.