Where can you learn more about the Quran reliably?

A sturdy way to learn about the Quran is to use not one source but a few that check each other. Start with the text. The 1924 Cairo edition is the dominant print edition today and follows the Hafs reading. Its orthography is largely, though not entirely, faithful to seventh-century manuscripts.

Next, a translation with notes. Arberry's The Koran Interpreted is the scholarly standard among English translations, while Yusuf Ali's heavily annotated version and Pickthall's are among the most popular with English-speaking Muslims. The Study Quran (2015) gives a translation with traditional interpretations of each verse drawn from several dozen exegetes. Ask who stands behind a translation: the free Saudi Hilali-Khan version, for example, has been criticised for being in line with its sponsors' interpretation.

Then a classical commentary, chosen for the question. Al-Tabari gathers many reports and older opinions; Ibn Kathir is a favourite of many modern Sunni Muslims, especially Salafis; al-Qurtubi concentrates on legal rulings; al-Jalalayn is brief, one volume. These four are Sunni works. Shia tradition has its own classics, such as Shaykh Tusi's al-Tibyan and Shaykh Tabarsi's Majma al-Bayan. Check which tradition each commentary belongs to: Sunni, Shia, Sufi and Mu'tazila commentaries each stress different things. Finally, an academic commentary, such as Reynolds in English, Neuwirth in English, or Le Coran des historiens in French, for historical context.

One last honest note: a critical edition of the Quran does not exist yet, and only about 300 of some 2,700 known commentaries have been published. So treat any single source, this lesson included, as one voice.