Related to your query, I suggest you follow https://www.youtube.com/watch?v=OdqDFvXGLRY

http://www.cgl.ucsf.edu/cytoscape/cluster/clusterMaker.shtml

Good Luck

Simply, attach to any element of the cluster a biologically significant label (e.g. pathway at which the gene pertains in the case of genetic networks having single genes as nodes, or academic degree of each single person in the case of a social network, hydrophobicity value in the case of a protein contact network having aminoacid residues as nodes..) and then check by an inferential statistics approach (chi-square or Fisher exact test in the case of categorical labels, kendall correlations in the case of real values or rank label) the significance of the correlation between the cluster each object perains to and the label.

..the clusters can be extracted (for future labeling oth their eleemnts with relevant properties of the nodes) directly by network structure by means of:

Article GIANT: A cytoscape plugin for modular networks