There are many cryptocurrency exchanges that don't accept real money (because then they'd be subject to regulation), so to trade there, you need to buy some cryptocurrency elsewhere and move it there before you can trade.

Many sites recommend buying Litecoin or Ether for that rather than Bitcoin, exactly because Bitcoin is so impractical. Bitcoin is failing as a currency even in the cryptocurrency market.

Recently there was a bitcoin conference that stopped accepting bitcoin as payment because processing was too expensive.

Cryptocurrencies might become mainstream payment systems some day, but it's not going to be Bitcoin. Ether is probably the most likely candidate.