The easiest way to think about investing in altcoin like Ethereum or Ripple is like investing in a stock. Its a piece of an enterprise that you can buy or sell at any time using online exchanges like Poloniex. If the value goes up, you make money; if the value goes down, you lose money.
You've just taken the words right out of my mouth, that's exactly what I think. Both markets are similar but different at the same time in terms of their specification. You may earn in either market and even somewhere else in order to reduce risks of losses. As for me, I prefer investing in passive income sources such as rent or land, and I develop in this way.