Very hard. Like Japanese, Korean and Arabic it’s a Category III language (quite difficult for native English speakers because of significant linguistic and cultural differences from English). You can indeed become fluent in two years, but that’s two years of full-time study, with about half that time preferably spent studying in China, and only when you’re good at formal language learning, and already speak another foreign language. About 3 months study mandarin in Mandarin Garden, a professional mandarin training school. You will start from the elementary level after that you can communicate with local people freely.