How to add your signature to Gmail:

After copying the signature, open Gmail in your browser and click the gear icon in the top-right corner. Select "See all settings" from the dropdown.

In the "General" tab, scroll down to the "Signature" section. Click on "Create new", give your signature a name, and then paste the copied HTML signature code into the editor.

Finally, scroll down and click "Save Changes" to update your signature.