Assuming that you are interested in performing a spectral clustering a good place to start would be here. I have attached a few files in which I implement one spectral clustering technique on some concentric circles as an example. The idea is to show how this works in a low dimensional space.
The Graph Laplacian can be calculated using the functionality of MATLAB graphs. This has a built in method, Laplacian which you might find useful. If the network is large you may need to implement another method.
Best of luck.
