What about percentages more than 100%? Well, sometimes percentages like these don't make sense. For example, you can't spend more than 100% of your time playing basketball, no matter how much you love the sport; 100% is all the time you have, and there ain't no more.
100% means "100 out of 100" — in other words, everything. So when you say you have 100% confidence in someone, you mean that you have complete confidence in them.
But a lot of times, percentages larger than 100% are perfectly reasonable. For example, suppose you own a hot dog wagon and sell the following:
10 hot dogs in the morning
30 hot dogs in the afternoon
The number of hot dogs you sell in the afternoon is 300% of the number you sold in the morning. It's three times as many.
Here's another way of looking at this: You sell 20 more hot dogs in the afternoon than in the morning, so this is a 200% increase in the afternoon — 20 is twice as many as 10.
Spend a little time thinking about this example until it makes sense.