Translation:You have to download the Duolingo app.
He/she certainly may; it is called "bait and switch" in retail. Or the free ad-soaked app may be termed a loss-leader. Regardless, a word-of-mouth recommendation is the most persuasive pitch there is. It's how I landed here...
As a native, “我要” means “I want” and “I have to”, although we can express the second meaning by saying “我得” (得 is pronounced as děi). But “你要 + 动词。” means advising (you have to do sth.). But (another “but”) “你要…吗？” means “Do you want …?”. In this case, 你要 can only mean “you have to”, because this sentence is an advice to the user. Maybe there are some mistakes though.