People have made lots of money with bitcoin, no it's not a Ponzi scheme you sell it just like anything else. Imagine that it's a piece of gold, just virtual.
Although it is really called the digital gold sometimes, it has nothing in common with the precious metal. Bitcoin volatility makes it unstable, and we never know if it goes up tomorrow or down.
But the volatility of bitcoin allows us to earn it much faster than gold. In addition, we can invest in both proven gold and modern digital bitcoin technology.