First, if you have a domain make sure you have a preferred site address selected. In the site editor, go to the 'Admin' tab > 'Site Address' in the left sidebar and choose a preferred site URL from the dropdown box.
Click 'Add A Property' > 'Add your site URL' (the preferred site address).
Note: The preferred site address does not need to begin with 'https' as the field suggests and can begin with 'http' instead.
Select the ‘Alternative methods’ tab and choose ‘HTML tag’, then click 'Verify'.
Copy the full strip of code and log into your site editor in a separate window.
Go to the 'Services' tab and click the 'Setup' button under the Webmaster Tools section.
Paste the code and click 'Save'
You should see a green tick in the box. Finally, go back to the Webmaster tools page in Google and click 'Verify' to complete the setup.