You will have to first register for the Sales tax number ( which can also be used to help you in a number of other documentation) . As recruitment comes under the service tax cloak.
It can be applied and will take appox a week to come to you. You then can quote the service tax number on your invoice and charge the same from your client. If you do not have a service tax number, you cannot charge the client for the same.
Please note that Service tax filing is a compliance issue and the sooner you get it the better.
Best wishes to you in your venture.