Strong
い adjective
This is a single kanji with an い on the end, meaning you know it's probably an adjective. What's the adjective form of strong? It's also strong.
つよい
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you: So you wanna be strong huh? Well, all you have to do is eat these two yogurts (つよ). One is filled with horse steroids, the other is full of bull steroids. They will make you so strong.
全日本の女子バレーチームは、中々強い
All Japanese women's volleyball teams are strong.
同点だったということは、両方強いチームだったということだ。
The fact that it was a tie means that both teams were strong.
風が強いから、今日は外に出るのはやめた方がいい。
It's very windy today, so it's better not to go out today.