There are many tool like Inter pro, Smart, Pfam, Threadom, Globplot and prosite. you can use any of them but their algorithm is different. prosite will tell you that your protein is having this particular domain and specific activity of your protein is being directed by this domain. it will tell you signature pattern of your domain. If you want structural information, you can go through Interpro and smart server.

NCBI Blast. Run protein blast search which runs conserved domain (CD) database search in parallel. In the results page on top you will see the functional domain(s) of the protein. 

@Ajeet and Avinash: Thank you for your quick reply, I will try those and will come back.