You can buy a fraction of a coin. Term "coin" is just a label. It could be tiny fraction, say 0.0001. So if you want to buy $50 of Litecoin (LTC), you would go to coinbase.com and buy with your USD, $50 worth of Litecoin and you can do with what you want with it. You can keep it there or send it to software wallet you have on your PC or your smartphone.
RE: Central Bankers Admit Cryptocurrencies Are A Threat To Their Existence - Episode 1508a