Nine 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 nine plus つ. So, this one is nine things.
Since all of the "number of things" words all follow the same pattern (number plus つ), you really just have to remember the part before the つ (and then remember that the つ is in all of these). All of the readings are the kun'yomi reading, which means we'll have to use a mnemonic to remember them (you know the on'yomi reading of the kanji portion).
What thing do you have nine of? The nine things you have are nine coconots (ここの). As you can guess from the spelling, coconots are not coconuts. Think of them as… fake coconuts. Imagine yourself juggling nine coconots in the air. Try counting them as you do, arriving at nine things. Then arrange them into a square on the ground. Three coconots by three. Now you should remember how to read 九つ.
このエリアに九つの山がある。
There are nine mountains in this area.
ドーナツを九つもらった。
I got nine donuts.
三人しかいないのに、大きいベッドを九つもオーダーしてしまった。
There are only three of us, but I accidentally ordered nine large beds.