Dear Manal,  

I am not sure what you really want to know here.  But, a simple look at the molecule would tell you if there is sigma contribution or pi contribution.  Also,  am not sure if you ate referring to complexes or pure organic materials.  You need to make your question clear on what you want to know.  

see the file

The simplest way, I think, is to start with two p orbitals. The sigma bond is formed when only one part of each p orbital is shared. On the other hand, the pi orbital is formed by an overlap of both parts of each orbital. 

The attached link has a good and simple explanation. 

https://sites.google.com/site/ed350201003/Task