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.|