The simple answer is that just like a dollar can be split into 100 pennies, a Bitcoin can be sub-divided into smaller pieces. But with Bitcoin, you can split a single Bitcoin into 100,000,000 units. So the answer is yes, you can buy a part of a Bitcoin.
These units are called Satoshis, and they are the smallest possible unit of Bitcoin. In theory, you can buy as little as one hundred-millionth of a Bitcoin. However, that would cost far less than a single penny and because a penny can’t be split it’s not realistic to buy such a small amount of Bitcoin.
Unit bias is a common investing bias where investors are tricked into thinking they are getting more value by purchasing coins with a lower per-coin value. Investors can easily get intimidated by the price of Bitcoin, and instead may opt for a coin with a smaller per-coin value. They believe they are getting a better value with more coins, but there is actually no relationship between the price of a coin and the value of that coin’s network. You must consider not only the price of a coin, but the total supply of coins in a given network to get a good estimate of a network’s value.