The speed dial feature of Opera will display your Favorite webpages each time a new tab is opened.
A simple click on one of these thumbnails will open the website assigned to it, a real time saver (reminds me of Google Chrome).
The speed dial is configurable in many ways and below you shall find some tips about it.
Configuring the Speed Dial Layout
You can choose the number of Website thumbnails to be displayed in the Speed dial interface.
Open Opera/ New empty Tab.
Click on the Configure Speed Dial button.
You can now choose between the layouts.
Add a background image to the Speed Dial
Simply check the Enable background image option and click on the Choose button, to browse your disk.
Or simply hide the Speed Dial feature.
Once you have set the Layout click on the Ok button to save your changes.
It still remains to assign the URL of the websites (if they aren't already in your Favorites of course).
To to this right click on any of the thumbs on the Speed Dial.
Click on Edit.
A window shall open and you shall have a text area "Enter Web address here"
Simply copy/paste the URL of the website in there and click on the OK button
There's a bunch of options provided in the text area allowing you to assign thumbs to the most recently opened URL: