There's no Wishpicks app to download from the App Store or Google Play. Instead, you can add the Wishpicks website to your phone's home screen from your browser — it then opens full-screen, like an app.
Steps
Open wishpicks.com in your phone's browser.
Use your browser's own menu to add it to your home screen:
iPhone (Safari): tap Share, then Add to Home Screen.
Android (Chrome): tap the menu (three dots), then Add to Home screen or Install app.
Tap the new Wishpicks icon on your home screen to open it full-screen.
For more detailed steps, open wishpicks.com/features/mobile on your phone.
What to expect
There's no native app and nothing to download. The home-screen icon is basically a bookmark that opens Wishpicks in full-screen mode — it works like an app without an app-store download. Wishpicks won't prompt you to install it either: adding it to your home screen is a manual step in your browser, and there's no in-app "Install" button.
This isn't an offline app, so you'll need to be online to use it.
Everything's the same as on the web. You sign in and use all the same features. See "Do I need an account to use Wishpicks?".