Arbitrarily, SLV, which is an ETF that tracks silver futures. If you want to play with fire (and learn a lot of cool stuff), trade options (that's what I used to do)
Websites: SeekingAlpha (side note: financial articles, SA included, are sophisticated-sounding babble put out by someone that has to meet their quota, not well-thought-out logical explanations by people in-the-know)
Make a list of terminology and learn directly what it means to your trading. Pretty much any trading term that has general meaning and isn't arcane and quant-y is googleable. I recall Khan Academy also having very useful videos explaining a lot of terminology (Salman Khan used to be a trader)
For example, in SLV: Liquidity: How easy (read: cheap) it is to open and close a position. If the spread on an option is $33.00 (sell) and $33.33 (buy), you lose 1% (most people say $0.33 - I prefer to look at the percentages) just by getting in and out of a position regardless of your trade (I'm ignoring commissions), and assuming the trade reliably goes through instantly. The higher the cost (time, risk of nonfulfillment, money) of opening and closing a position, the more illiquid the position is.
In the context of houses, the time and effort and money put into maintenance and time and uncertainty involved in buying/selling, etc make them extremely illiquid investments. If you own AAPL stock and it crashes, you can hit a button and sell it. If you own a house and the housing market collapses, good luck!
If I were to invest the cost of a house in some high-volume stock with a tight bid-ask ratio and sell it two years later for the same price by hitting a button on my phone, my losses are just the bid-ask difference and I was never really at much risk of being unable to sell it instantly (during market hours at least). It's a very liquid position.
That's just one example, but there are plenty out there. Jump in feet first, google all the things, and don't wager stupid amounts of money.