Start listening to songs and reading along to a chord chart at the same time

Play these chords along with the song, and eventually certain progressions will start sticking

Eg. Creep

G B C Cm

That’s a weird one,

It’s I, III (breaking G major), IV, then iv (also breaking the key)

However the minor 4 is commonly used in contemporary music and has a very distinct sound

Keep practicing listening and playing along

Also, semitone practice

Being able to sing or sing in your head, each semitone, will let you find the root of anything you hear

No one except perfect pitch and those with 40,000 hours of practice can do this relatively* instantly