I’ll second Fiddle’s (second fiddle… LOL!) post. Get familiar with the 1, 4, 5 in as many keys as possible. Also learn the 6, which is most often the minor, and the major 2.
Theory time. I say MAJOR 2 because if you look at the scale of the given key, the 2 is technically a minor. Take G, for example. Your scale is G A B C D E F#. The 1 (G) is G B D. The 2 (A) is A C E. The C in that chord makes it a minor, since the chord of A is A C# E.
I hear you asking “So why do we play a MAJOR 2 so often in songs?” This blew my mind the first time it was explained to me. A major 2 is the 5th of the 5th. So A is the 5th of D, and D is the 5th of G. When the ear hears that A, it begs for resolution to the D and then begs again for the G.
Ray Stevens used this like crazy. Several of his songs were played as 1 - 6 - 2 - 5, or 1 - 5th of the 5th of the 5th - 5th of the 5th - 5th.
It’s not very often you hear a 3rd thrown in, but if you want to hear what it sounds like, check out Battle Hymn of the Republic right at the 16 second mark. https://banjobenclark.com/lessons/the-battle-hymn-of-the-republic-banjo
As Fiddle said above, in this song, it’s being used to lead your ear into the 6 (minor.)