When buying coins, and especially with Bitcoin, you will notice that your purchase is in decimal. A Bitcoin itself is relatively expensive, around $10,000 at the moment (as of 15th Feb '18). If you were to purchase say $5,000 of Bitcoin, you would at today's rate be purchasing around 0.5 of Bitcoin. Do not ever worry about this; Bitcoin operates at eight decimals places. You do not need to own a whole Bitcoin or any coin for that matter. Consider it like pence in the pound or cents in the dollar, but with more decimal places.
Only invest what you can lose. During the recent crash in January 2018, hobby-investors got burned. Reports of frustration and losses came at the cost of broken monitors, smashed laptops, and heavy monetary losses. While the rules are in more particular order of importance, it’s safe to assume that this is the most important rule, the rule to rule the rules. As soon as your money is converted into cryptocurrency, consider it lost forever. There is absolutely no guarantee you can get it back. Losses don’t simply come from dips in the market; extraordinary factors such as hacks, bugs, and government regulation can mean you’ll never see any of your money again. If you are investing money you can’t afford to lose, you need to take a step back and re-evaluate your current financial situation, because what you’re about to do is an act of desperation. This includes: using credit cards, taking out mortgages, applying for loans, or selling everything and traveling the world (as glamorous as that sounds).