• 九ここのつ — nine (generic counter)
• 九人きゅうにん — nine people
• 九時くじ — nine o’clock
• 九月くがつ — September
• 九州きゅうしゅう — Kyushu
• 九九くく — multiplication table

“九” is simple but very common. You’ll see it in time (九時), months (九月), place names like 九州 (Kyushu), and even school math as 九九 (the multiplication table).