Apple has announced that they will be releasing the public beta for iOS 10 and macOS Sierra. This means that as long as your device is registered, you will be able to get your hands on the public beta versions of the software. However note that because they are still considered to be beta, you shouldn’t expect too much.
As the whole point of beta is to test the software and fix bugs that users come across, there is a good chance that some features might not work the way it was intended, so obviously using the public beta of iOS 10 or macOS Sierra as your daily driver is probably not the best idea, at least not unless you have a spare device that you can use to test the softwares on.
That being said, both iOS 10 and macOS Sierra are expected to be officially released later this fall, but for those too curious to wait, we guess the public beta could be a good way to sate your curiosity.