1. Explain it simply
关于 means 'about / regarding' and introduces the topic of a sentence.
Put 关于 + topic at the START, then a comma, then your comment: 关于这件事，我不太清楚。
The 关于 phrase names what you're talking about; the main point comes after it.
关于 always comes before the topic, never after it (这件事关于 is wrong).
2. Show examples
关于这件事，我不太清楚。
Guānyú zhè jiàn shì, wǒ bù tài qīngchu.
Sandhi:Guānyú zhè jiàn shì, wǒ bú tài qīngchu.
About this matter, I'm not too clear.
关于 + topic at the front
关于这个问题，老师会讲。
Guānyú zhège wèntí, lǎoshī huì jiǎng.
The teacher will explain about this problem.
comma then comment
关于健康，医生说了很多。
Guānyú jiànkāng, yīshēng shuō le hěn duō.
The doctor said a lot about health.
topic first
3. Share a tip
关于 leads the sentence to set the topic, followed by a comma. Don't put 关于 after the topic (这件事关于 is wrong) or at the very end.