E-commerce operators who are required to collect tax at source (TCS) under GST must obtain GST registration. The following are the steps for GST registration under e-commerce:

1. Go to the GST portal (www.gst.gov.in) and click on the 'Register Now' button.

2. Select the 'New Registration' option and choose 'E-commerce Operator/Tax Collector' as the type of taxpayer.

3. Fill in the necessary details such as legal name of the business, PAN number, state of registration, and email ID.

4. You will receive an OTP on the registered mobile number and email ID, which needs to be entered on the portal.

5. After the OTP verification, a temporary reference number (TRN) will be generated, which needs to be used for the next steps of the registration process.

6. Log in to the GST portal using the TRN and fill in the remaining details such as business details, promoter/partner details, authorized signatory details, and bank account details.

7. Upload the required documents such as PAN card, proof of address, bank statement, and photographs.

8. Submit the application and obtain the Application Reference Number (ARN).

9. The GST officer will verify the application and if there are no discrepancies, the GST registration certificate will be issued.

It is important to note that e-commerce operators must also file GST returns such as GSTR-8 for TCS, GSTR-9 annual return, and GSTR-9C reconciliation statement.