The kanji and the word are exactly the same. That means they share meanings as well.
This word is used to say things like "a high number" and "the number of students".
Since this word is made up of a single kanji, it should use the kun'yomi reading. When learning the kanji, you didn't learn that reading, so here's a mnemonic to help you with this word:
Imagine yourself counting by playing a kazoo (かず). Each number you count, you toot your kazoo. How fun!
What is the number of tomatoes in this soup?
This time, the number of deaths was the same as last time.
In Japan, the number of babies being born is decreasing.