Eight Things
numeral
This word follows the "number of things" pattern where there's a kanji for a number plus つ on the end. Whenever you see this, you know the word means "____ things." Knowing that, as long as you know the kanji (which you do) you can figure out what number of things it is. For this one, it's the kanji for eight plus つ. So, this one is eight things.
Since all the "number of things" words follow the same pattern (number + つ), you just have to remember the part before the つ. All their readings use kun'yomi. So far you've only seen the on'yomi reading for this kanji though, so here's a mnemonic to help you remember it:
Can you think of eight things that start with the sound "ya"? Yah (や), you can. Try listing them out loud. Even if you don't manage it, you'll remember the connection between eight and "ya."
Oh, and see that small っ in the middle of the reading (やっつ)? It puts a little emphasis on the consonant that follows it, like yattttttsu. OK, not that much emphasis. More like yattsu.
八つの山
eight mountains
八つのキーワード
eight keywords
八つのタイプ
eight types
このカレーにはじゃがいもが八つ入っています。
This curry has eight potatoes in it.
キットカットが八つ、口に入ってます。
There are eight KitKats in my mouth.
うちのおばあちゃんはインスタグラムだけで八つもアカウントをもってるんだ。
My grandma has eight accounts on Instagram alone.