We can turn a verb into a noun by adding the nominalizer particle の after the plain form of the verb. We can then use the verb in constructions where we normally would use a noun.
One thing this allows us to do, is to express that we are good at or bad at a certain activity. To say that we're good at something, we simply use a verb in the plain form + のが上手. Similarly, if you don’t like something, you can use plain form + のが下手.
We already knew how to say he is good at Japanese. Now we're also able to say he is good at speaking Japanese.
He is good at Japanese. | 彼 は 日本語 が 上手 です。kare ha nihongo ga zyouzu desu. |
He is good at speaking Japanese. | 彼 は 日本語 を 話すの が 上手 です。kare ha nihongo wo hanasuno ga zyouzu desu. |
(I)'m not very good at eating with chopsticks. | 箸 で 食べるの が 余り 上手 じゃ ない。hasi de taberuno ga amari zyouzu zya nai. |
(I) am bad at playing the guitar. | ギター を 弾くの が 下手 です。gitaa wo hikuno ga heta desu. |