Grammar · な-adjectives
上手 and 下手, good and bad at
[Thing] が上手です / 下手です
Skill also takes が. 上手 about yourself sounds boastful, so use 得意 or simply say you like it.
The mistake to avoid
Complimenting someone with 上手ですね is normal and expected. Accepting the compliment is not; deflect it.
Examples
彼は料理が上手です。
かれは りょうりが じょうずです。
He is good at cooking.
私は歌が下手です。
わたしは うたが へたです。
I'm bad at singing.