N5
のがへた
To be bad at, Poor at, Unskillful
私は漢字を教えるのが下手。
I am bad at teaching kanji.
Explanation
「〜のが下手だ」 means you are not good at doing something: 「私は料理を作るのが下手です」 (I'm not good at cooking). Form: dictionary form + の + が + 下手. Said about yourself it sounds modest, and it also states plainly that your skill is low.
Mixed up with
「下手」 is about technique and skill being low; 「苦手」 also means 'it's a headache, not to my taste, I feel resistance': 「納豆が苦手です」 (I can't stand natto), 「人前で話すのが苦手です」 (I get nervous speaking in front of people).
Saying 「〜のが下手ですね」 to a boss, an elder or a stranger's face is very rude.