Used with に to mark a topic: ～について means 'about ～'. Formal and neutral; common in speech and writing.
Let's discuss this issue.
彼は日本の歴史について詳しい。
He is knowledgeable about Japanese history.
Derived from the verb 就く (つく, 'to take a position, to follow') in its te-form, but now used as a fixed expression meaning 'about' or 'concerning'.