If you are on the 18.104.22.168 version of the app, you can turn on WARP with the "enable" button on the lower right of the screen. Or, tap the hamburger menu on the top right, then select "22.214.171.124 with WARP".
To try WARP+, our limited data plan, you simply have to refer people to download the 126.96.36.199 app. To do this, tap the Share button on the home page of the app, or tap the hamburger menu on the top right and tap "Share to get 100MB free each month".
To subscribe to WARP+Unlimited, you can purchase a subscription. The price for the subscription is located on the button at the bottom of the 188.8.131.52 app home screen. Tapping that button will bring up a dialog for you to confirm your subscription. All payments are handled by the Google/Apple app store, and the payment information associated with your Google/Apple account will be charged for these subscriptions.