the default browser will either be called Chrome or Internet, and you can find it in the app drawer or as a shortcut on one of the home screens. the app drawer will be an icon of little squares or dots on the dock.
in the Chrome web browser, there is an icon of a aquare with a number inside it, and a square behind it, those are the windows. should be similar in the other browser. it will display the windows, with an x at the top-right corner, just tap the x for each window.