All users need to do to take part in the public beta is to ensure that they have the proper profile setup on Apple’s beta software website before downloading the software, once that’s done, they’ll be able to install it. However, do note that because this is the first public beta, there are bound to be bugs and incompatibility issues that you’ll run into.
This means that it’s probably not the best idea to use it as your daily driver or on your main computer in case something goes wrong. This is more to give users an idea of what to expect and if they’re so inclined, provide feedback on features and also bugs so that Apple can iron out the kinks ahead of its release.
macOS Monterey is expected to be released later this year, possibly in the third-quarter of 2021 as we have seen in the past, so this is just but a glimpse of what we might be able to expect.