The Bogleheads′ Guide to Investing

Highly recommended if you're new to investing. The author offers sound advice that helps you learn how to actually invest your money and not gamble it away. Great advice in general though keep in mind that this is US-centric, but the principles they discuss will apply regardless of your nationality, you might just have to find different index funds or methods to access them, but the Boglehead community already provides an answer for that online for non-US investors.