To register as a buyer on GeM, you need to visit the GeM portal and click on the "Register" button. You will be required to provide some basic details such as your name, email ID, mobile number, and PAN number. Once you have provided the required details, you will receive an OTP on your registered mobile number. After entering the OTP, you will be directed to the buyer registration page where you need to fill in the necessary details and upload the required documents.