Bitcoin has captured America’s imagination. Whether or not the cryptocurrency will ultimately turn out to be a good investment or just a passing fad remains to be seen. Indeed, in the past several months Bitcoin prices have enjoyed a run-up that makes the 1999 tech bubble look staid by comparison. That excitement — the promise of sudden riches or sudden ruin — has a lot of people wondering how a bitcoin investment actually works. If that’s you, here’s a step-by-step guide on how to trade...