The sign up form asks users to enter a Google Account email and the mobile OS they are using. Ingress players have the ability to enter their Agent Name and Level. Signing up does not guarantee entrance into the field test and there is a long list of warnings to note. Players also have to agree to a confidentiality agreement.
Field testing is open to the United States, Australia, or New Zealand and requires an Android device running 4.3 or higher or an iPhone 5 with iOS 8 or above.
Source: Pokémon Go/Niantic Labs