Apple released public beta versions of their two main operating systems today. The developer betas have been available since the Worldwide Developers Conference earlier in the month.
Those interested should go to the Apple Beta Software Program site and sign up there. Note that beta software often contains bugs or incomplete features and anyone using their Mac casually or for work should wait until the final version of Catalina comes out in the fall. However, those with perhaps an extra Mac that can spare can use this as a chance to preview the new features while they also help out Apple with feedback.