Last week, Apple released the second beta of iOS 11 for developers. Unfortunately, those who want to take these builds for a spin need to pay $99 USD for a developer account. However, today the first public beta became available, and anyone interested can download and install it for free.
The schedule appears to be the same as previously announced - Apple plans to launch the final version of iOS 11 this fall, but until then regular public betas will be delivered to the masses. Those who choose to install iOS 11 beta will get the new betas automatically and, once the final build arrives, their devices should be automatically updated to that version.
Since it happened more than just a few times to see beta iOS builds to behave as they should not (iPhones simply refusing to boot after installing such builds, for examples), it would be a good idea to avoid installing an iOS beta on the primary iPhone or iPad.