Tabbed browsing is one of the more useful features to make it to Web browsers. However, as with using single windows you might inadvertently close one and need to restore it. While you can create a new tab and then peruse the browser history to find a link to the content it contained, an easier option is to use the built-in tab restoration options in your browser.
To do this, there are two hotkeys to keep in mind. The first is the classic Command-Z for undoing an action, which in Safari will undo a recently closed tab in a specific window; however, this only pertains to the single most recent tab closed. While this allows you to restore separately closed tabs in different windows, for a given window you can only restore the last closed tab.
On the other hand, alternative browsers like Chrome, Firefox, and Opera use a common hotkey, Shift-Command-T, for undoing closed tabs, but unlike Command-Z in Safari, subsequent presses of this hotkey will continue restoring other closed tabs.
In addition to restoring tabs sequentially, Chrome, Opera, and Firefox all have options to browse through collections of recently closed tabs for a given window, so you can quickly reopen either some or all of them. These options are available in the History menu for Chrome and Firefox, and in the Window menu for Opera.
Beyond managing tabs, you may also wish to restore entire closed windows. In this respect, while Safari has an option to reopen a recently closed window, as with its tab management it will only do so for the most recent window. On the other hand, Chrome, Firefox, and Opera manage closed windows as collections of tabs. This blends well with their existing tab management options to allow you to restore any set of tabs as a single window. These options are available in the History menu of Safari, Firefox, Chrome, and Opera.
While Safari only allows a single tab or window to be restored, this is not necessarily a hindrance--it just requires you to be on top of any inadvertent closures and quickly restore them when they happen. Safari's browser history and bookmarks should be enough to restore other recently closed content; however, if you need specific tab organizations or regularly find yourself needing to restore multiple tabs, then Firefox, Chrome, and Opera offer more robust options than Apple's Safari browser.