What is the difference between the Premier League, the FA Cup and the Champions League?
Three separate competitions that English clubs play in simultaneously, run by different bodies with different formats.
The Premier League is a league. Twenty clubs each play every other club twice, home and away, over 38 matches. Three points for a win, one for a draw. Whoever has most points after 38 games is champion — there are no play-offs. The bottom three are relegated to the division below, and three come up. It runs from August to May.
The FA Cup is a knockout tournament, and the oldest football competition in the world, first played in 1871–72. Any eligible club in the English football pyramid can enter, from Premier League sides down to small semi-professional teams — over 700 enter each season. Lose once and you are out. Because a lower-league club can be drawn against a giant, it produces the upsets the competition is known for.
The Champions League is European, organised by UEFA rather than the English FA. The strongest clubs from leagues across Europe qualify based on their domestic league position the previous season. It combines a league phase with knockout rounds and ends in a single final.
So a club can compete in all three in one season, which is why fixture congestion is a constant subject.
English clubs also play the EFL Cup (a second domestic knockout, sponsor-named), and the Europa League and Conference League are UEFA's second and third tiers.
Winning the domestic league, the FA Cup and the Champions League in one season is called the treble, and has been achieved by only a handful of European clubs.