What is Works Contract Tax ?

Please explain me what is works contract tax and also let me know whether it is applicable for maintenance contracts ? and also is it applicable for Manpower supply contract ?

Manpower supply is a service and service tax is levied for that but whereas why both service tax and works tax is applicable ? In Manpower supply contracts no goods are supplied, then why works tax ?

Suppose if the customer pays works contract tax (WCT) on behalf of us and give some certificate for that then how can we claim for that ?

Also let me know whether VAT TIN No. is used for WCT also ?

Please explain me in detail...!!

thank you...!!