Percent can be a handy tool. The word literally means "for hundred", and that's exactly how it's used. It's a ratio that says how often something will happen out of every hundred times, or how many things have a certain quality out of every hundred people. I'm not going to belabor defining percents because they're ubiquitous; it's hard to not know how they work.
What's easy to forget, though, is how misleading percentages can be. If I went to Yankee Stadium and told the crowd that ten percent of them wouldn't make it home tonight, people would be reasonably confident that they would be in the 90 percent that would be fine. If I went there and said that 5,000 people weren't going to make it home, that would cause a lot more panic. Five thousand is so many people that it seems a lot more likely that you would be picked. But in reality, it's the exact same situation.
Percentages can make big numbers look small. They can also make small numbers look really big. If you go from having two dollars to have four dollars, you just increased your money by 100%. Better yet, you now have 200% of what you started with. Those are mighty large percentages, but they represent a measly quantity.
Being accurate isn't always enough when it come to numbers (much like with words). You need to find the method that not only conveys correct information, but also expresses the intended understanding of what those numbers mean.