Safari is the default and more commonly used Web browser in OS X systems, and while a fairly robust browsing solution for Mac users, it can encounter periodic problems that cause high CPU usage or a hang, or other odd behavior that may be frustrating to manage.
If this happens, then as is the case with all versions of Safari, you can try quitting and re-launching it, closing windows, or more in-depth troubleshooting like disabling plug-ins (globally or on a per-site basis), clearing caches, and clearing cookies and other site-specific data.
Unfortunately, when such problems happen, you may have numerous Safari windows open, which can make troubleshooting Safari problems a bit difficult, not only in wading through the clutter of windows, but when troubleshooting one you might inadvertently close others that are working just fine and interrupt your workflow.
You can peruse through your Safari windows and try to find the misbehaving one manually, but in OS X Mavericks you can use Activity Monitor to isolate which window is causing the problem.
With the latest versions of Safari, loaded Web pages are collected in groups of separate running processes, which helps keep others stable if one goes awry. Unfortunately each of these processes is similarly named Safari Web Content, which in systems prior to Mavericks does not help in tracking down what might not be working properly (for instance, if a specific site is loaded and causing the hang). In Mavericks, Apple has a quick way to see what pages are loaded in what process.
To do this, open Activity Monitor and perform a search for "Safari Web Content" to isolate the running processes, and then sort by CPU usage or other method for locating the one giving you problems.
With the problematic process located, simply hover your mouse over it and you will see a tooltip box appear that contains the URLs for the pages loaded in that process. Unfortunately you cannot click the links in Activity Monitor or otherwise trigger the corresponding window to come to the front, but you can use the link information to identify the potential Safari tabs that contain the problem. Simply review your windows, see which contains tabs for the links in the tooltip, and you can try to manage it without quitting and relaunching Safari, or more intrusive troubleshooting steps.
While this tip is useful for Safari, it should work for other processes that use WebKit, including "Content" processes for the App Store, though these may be more limited in scope (as in, the URLs of the App Store only) and not as useful for troubleshooting.