Get Familiar with the Beta Installation Process
If you're new to Apple's beta program you'll want to familiarize yourself with the installation process before downloading the iOS 12 beta.
If the process feels intimidating, you might want to hold off on an install until you feel confident in your abilities.
If at any point during the installation you start to feel uncomfortable, stop. The iOS 12 beta isn't going anywhere and you've got until now and September to try it.