At the top of your browser is the tab bar. Your browser can have multiple tabs open at a time, each of which displays a different web site.

A browser with three open tabs
This browser window has three tabs open

Want to visit another website without closing the one you’re currently using? Just click the new tab button:

A browser with three open tabs and the new tab button circled

Done with one of your tabs? Click the close tab button:

A browser with three open tabs and the close tab button circled