It's not something you can access...it's kind of like asking how do you access the gyroscope. You can't, you can only see it's functionality and options within apps that take advantage of it.
Also remember it is always tracking and saving that information in the M8 chip. So if you download an app that needs that information it will be presented since the day you started using the iPhone. The only way it resets is memory (I have not tested this one yet) or set up as new phone.