You can download the new Mac operating system for free right now
Most Macs will be able to get the update, but you can click here to see if your computer is compatible.
Sierra isn't a major overhaul of the operating system, but it does have loads of smaller features that add up to a decent update. It's also free, so you don't have to worry about wasting your money.
The biggest change is Siri, which is coming to the Mac for the first time. In addition to all the normal Siri stuff from the iPhone, Siri for Mac can also search for files on your computer. It's also a pretty decent web search tool.
Other features coming to Sierra include: Apple Pay on the web, picture-in-picture for web videos, a new Photos app, and a revamped version of iMessage.