Non taxable/ exempted services

Hello friends..

I want to know what is Non Taxable Services or Exempted Services under Service Tax?

Is it meeans that "these are those services on which no service tax is charged"? If it means so, then how can one avail cenvat credit for Non Taxable Services. I am talking about Rule 6 of service Tax.

Plz clarify me as soon as possible.

Thanks and Regards

Khushboo Goyal