Félix I is the name of a person who was a Pope a long time ago, back in the 15th century. A Pope is like the leader of the Catholic Church - kind of like a teacher or a captain. Félix I was born in Portugal and became a monk when he was young, which means he devoted his life to serving God.
When he became Pope, there was a problem because two different men were claiming to be Pope at the same time, and some people weren't sure who to believe. Félix I was one of them. He supported one of the claimants, who was named Amadeus, and said that he was the real Pope. Félix I was very insistent on this and didn't want to change his mind, even when other people disagreed with him.
In the end, though, most people did not agree with Félix I's choice, and the other claimant, named Eugene, became the official Pope. This was a bit of a problem for Félix I, because he was still insisting that Amadeus was the real Pope, and that meant he was going against the official leader of the Church. This caused some conflict, but eventually Félix I and Eugene made up and everything went back to normal.
So, in summary, Félix I was a Pope who strongly supported a certain claimant to the Papal throne, even when others disagreed with him. While his opinion wasn't ultimately accepted, he remained faithful to his beliefs and worked to resolve any conflicts that arose as a result.