Clear your cache and delete cookies; see links below. You can click on any menu item (Income, Deductions, Health, etc) at the top to get out of a stuck screen. If you keep having an issue, try logging out and logging back in using a different browser. Your browser stores recently visited web pages as temporary files in a cache, which enables the pages to load up more quickly when revisited.
However, a full or corrupted cache can cause various problems in TurboTax, so sometimes you need to clear your cache (that is, remove these temporary files).
Here are the official instructions for the most popular browsers:
Apple's official support site doesn't appear to contain instructions for clearing the cache in Safari. Your best bet is to search the internet for clear Safari cache or similar search terms.
