If you are not already on the original home page of Opera, click on the icon marked
with red on the top left corner

Click on the icon on the top right corner

Scroll all the way down and click on Go to browser settings

Scroll all the way down again and you should find the On startup section. Choose the
(Open a specific page or set of pages) and click on Add a new page. Type in
ponnahduslauta.fi and click on add. You are now done and can leave the page