Article: It's the icon with two Roblox characters that says "ROBLOX" inside. You'll usually find it on the home screen or in the app drawer. It's near the top-right corner. Your current balance appears at the top. The price for each package appears next to the amount of Robux you're buying. The pop-up will appear, asking you to confirm your purchase. If you want to cancel the purchase, tap Cancel (iPhone/iPad) or the back button (Android). If you're using an Android, you'll be billed by your Google Play account. If you're using an iPhone or iPad, you will be billed by the App Store. Once you confirm, your Robux will be added to your balance.

What is a summary?
Open Roblox on your Android, iPhone, or iPad. Tap the R$ icon. Tap the amount of Robux you want to buy. Follow the on-screen instructions to pay for your Robux.