A fraction is a part of a whole number for example 1/2. 1/2 is a half of one whole piece and if you multiply it into any whole number whether it's 2,4,6,8,10...... basically, if you multiply a fraction less than one with a non-zero whole number, it will always be less than the whole number it's being cut into smaller pieces. However, if the fraction is greater than 1, we would technically have an answer greater than the whole number product, just something to remember.
"per" means "divided by" in this context. When you want "words per minute", it means you want the number of words divided by the corresponding number of minutes: