The meaning of the Straight Way

Q 5: In Surah Al-Fatihah, we read: Guide us to the Straight Way. The Way of those on whom You have bestowed Your Grace, not (the way) of those who earned Your Anger (i.e. those who knew the Truth, but did not follow it) nor of those who went astray (i.e. those who did not follow the Truth out of ignorance and error). Amen. I would like to know what is meant by the "Straight Way" and who are those whom Allah (Exalted be He) guided to follow it? Also, what is the meaning of Amen?

(Part No. 4; Page No. 186)  A: The Straight Way means the clear path in which there is no crookedness. Accordingly, it is interpreted as referring to the Qur’an, Islam, or the Prophet (peace be upon him). All these views are true. Anyone who follows the Prophet (peace be upon him) follows Islam, and who, in turn, must follow the Qur’an. As for "those on whom Allah has bestowed His Grace," Ibn Kathir stated in his Tafsir (exegesis of the meanings of the Qur’an) that Al-Dahhak reported from Ibn ‘Abbas that it meant: "The path of those upon whom You (Allah) have bestowed the blessing of obeying and worshiping You from the angels, the Prophets, the Siddiqin (the truly faithful), the martyrs, and the righteous." This is similar to the Saying of Allah (Exalted be He) in another Ayah (Qur'anic verse): And whoso obey Allâh and the Messenger (Muhammad صلى الله عليه وسلم), then they will be in the company of those on whom Allâh has bestowed His Grace, of the Prophets, the Siddiqûn (those followers of the Prophets who were first and foremost to believe in them, like Abu Bakr As-Siddîq (رضي الله عنه), the martyrs, and the righteous. And how excellent these companions are! Finally, the word Amen means: "O Allah, answer our supplication."May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.