Surah Al-Kafiroon was revealed to the Prophet Muhammad(saw) in the city of Mecca. One thing you should know about this surah is that the Prophet Muhammad used to read this surah a lot in his 2 sunnah prayers for Fajr. He would also read surah Al-Kafiroon a lot for the 2 sunnahs after Maghrib prayer. We should try and read surah Al-Kafiroon in our salah so that we can remember it!
Surah Al-Kafiroon talks about one time when the people of Quraysh tried to make a deal with the Muslims. They told Prophet Muhammad(saw) and the Muslims to worship their idol gods for one year and then they would worship Allah for one year. The Prophet and the Muslims said no to this deal. Do you know why? Its because we dont make deals when we worship Allah. We dont worship other gods even for one second, because Allah told us not to. We dont want to disobey Allah. It is very important to only worship Allah and not other things, and then Allah will be happy with us. So this surah tells us what the Muslims said about this deal the non-Muslims tried to make.