"Percentage" is a commonly used word, and it means a fraction expressed a hundredths. It is often expressed by using the percent sign, %
"This drink is only 10% juice and 90% water."
"When you flip a coin, it has a 50% chance of coming up heads."
"In Iceland, 99% of the population is literate."
"Percentile" is a technical term in statistics, expressing the relative position of something when a group is ranked by size. "He scored at the 68% percentile" means that 68% of those tested scored lower and 32% score the same or higher.