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.