The default behavior in Safari for opening links, bookmarks, and Web searches is to display the results in the current browser window; however, if needed then there are options for opening these in other windows, tabs, and otherwise augmenting your browsing experience.
As with many programs in OS X, Safari supports a number of hidden alternative behaviors to standard commands for opening pages and tabs. These can be invoked by using modifier keys, and in Safari, a few of these are specific for how links and searches are managed by the program. These will allow you to perform actions such as opening links in new windows but keep the current window in focus, or manage which tab is the foremost after opening a new tab.
In standard behavior, entering a URL in Safari’s address field will take you to that location, or entering text phrases will search for them in the default search engine in the current window, but you can supply the following modifier key combinations when pressing Enter in Safari’s address bar, to modify these behaviors accordingly:
Opening in new windows
Shift — Open URL in new window
Option-Command — Open URL in a new window behind the current one.
Command — Open URL in new tab, but keep current page in focus
Shift-Command — Open URL in new tab and switch focus to the new tab
Saving to disk
Option — Save URL source to disk (downloads folder)
These options will not only work in Safari’s search bar, but will also apply when you click a link on a Web page.
Lastly, with Apple’s approach to combine the search and address fields in Safari, you cannot easily search for URLs, since entering them will have Safari go to that URL’s address instead. This might have you first going to Google, Yahoo, or Bing, and then entering the URL string at these services, but instead you can also do this in Safari by encasing the URL in quotes, parentheses, brackets, or other container characters.