Good thing you're interested, there's something of a global economic tug-of-war going on right now. For the past ~70 years the $USD has been the reserve currency (the main thing the majority of businessmen felt content to denominate their trades in) but lately its power has been waning; better investment opportunities in China/Asia and other places are pulling wealth away from the US, and they're running out of tactics to retain it (eg petrodollar). We're probably gonna see a massive shift in the way whole COUNTRIES do business between each other so dumping all your money into an index fund would be incredibly foolish right now. You'd do well to just stockpile as much cash as you can for now, learn about what's going on, and be ready to snatch up some decent stocks at bargain prices once shit hits the fan.
I recommend reading James Rickards book 'Currency Wars', it's a pretty decent synopsis of what's going on today. Once you understand what's happening on a macro scale, read some books on security analysis to learn how to analyze a stock and whether it's over/undervalued, then invest accordingly.
Also start listening to the news, I particularly enjoy the 'Money for Nothing' podcast based out of Hong Kong. Follow ZeroHedge and some prominent traders on twitter, through them you'll find some tickers to look at and familiarize yourself with market fluctuations in regards to trading. Open an account with a brokerage and play with their trading platform, some of them come with no costs to open an account and even have a paper-trading demo that comes with the client you can play with.
I haven't traded any stocks myself so take my advice with a grain of salt, although I've been dabbling with the scene for the past year and am looking to get into it soon. Right now I'm just saving up my cash and waiting for the right opportunity to jump in. The US markets are looking retardedly overvalued, so I don't think it's too farfetched to expect some kind of huge correction in the coming years, just like back in 2008. If we do see something like that happen I plan to buy some stock in the most obvious companies, like Facebook and Google. I still need to learn some stock analysis though.