After sending exam fee to IEI, you will receive an sms (for this your mobile number should not be registered in DND registry of your mobile operator) stating that IEI has received your fee. A ref number will also be given.
About 15-20 days before start of exams, roll numbers and admit card appear on IEI website http://www.ieindia.info/ from where you can confirm your registration in exams. You can also check roll number at http://www.amiestudycircle.com/
You can take the print of admit card. This admit card alongwith identity card can be used in exam hall. However you can also collect original admit card from your local/state centre or exam hall. For this you must contact your local/state centre. For list of local/centres with phone numbers, click here