So many ways to configure. Opera is a browser. Similar to other browsers like Netscape, Mosaic, Internet Explorer, Amaya, and Konquerer.
Opera uses one main window to contain multiple webpages.
While you functionally max out other browsers after a few open webpage windows, Opera allows you to open dozens upon hundreds of sites and not clutter your task bar. On the fastest available machines, Opera is about a dead tie with some other browsers for load speed. The huge speed boost is not so much from raw page display speed, but in usability. You can easily surf most sites twice as fast with Opera as you can with other browser. Opera is HTML 4 and CSS2 compliant.