Step 1 : First one has to make sure that all the required documents are in hand to apply online. If you would like to know about the documents that are required for this procedure, please visit the following link : Required Documents for Paying Vehicle Tax Online
Step 2 : Please use the following link to reach the online portal : Online Portal.
Step 3: Now enter your vehicle registration number and chassis number in the text box highlighted in red in the image below.

File:Tel green tax 3.gif

Step 4: Enter your valid mobile number in the text box in the "Applicant Details" section. See tax details highlighted with red curly braces.

File:Tel green tax 2.gif

Step 5: Check the details for payment and click on the "Submit" tab.

File:Tel green tax 1.gif

Step 6: Follow the on-screen instructions and complete the payment process.
Step 7: Click the appropriate tab to print the tax token / green tax receipt. Keep it safe for future reference.