Is a scale a combination of chords or a combination of picking that go into chords?
Interesting question. The answer is "both", but that's confusing.
A scale is a collection of notes. The scale determines the key. "Key" and "scale" are pretty much the same thing. They both basically mean "the collection of notes from which most of the stuff in this song is drawn."
So the melody is (usually) made up of notes that are in the scale (in the collection).
The chords that underlie that melody are made up of multiple notes stacked on top of each other. For example, the C major chord is made up of three notes: C, E, and G. Usually, the notes in the chords in a song are all taken from the collection of notes that make up the scale/key of the song.
I'll repeat that another way, because it's important.
The chords in a song are (usually) made up of notes chosen from the same scale that makes up everything else in the song.
So, since the chords are made up of the notes from the scale, you can also look at it from the other direction and say that the notes in the chords are the same as the scale. It works either way. It's all one big collection of notes.
Here's a specific example. The C major scale is C D E F G A B.
A melody in the key of C will probably use some or all of the same notes: C D E F G A B.
Common chords used for songs in the key of C are the C major chord, the F major chord, and the G major chord.
The notes in the C major chord are C, E, and G. The notes in the F major chord are F, A, and C. The notes in a G major chord are G, B, and D.
If you pile up all the notes in those three chords and put them in order, what do you get? You guessed it: C, D, E, F, G, A, B... The C major scale.
JJ
P.S. It's not a hard and fast rule that melodies and chords always come from the scale/key of the song. Sometimes a song will go
outside the scale/key for part of the melody and/or for notes in a chord, just for the heck of it. You can think of this as a sort of temporary key change, or a quick "borrowing" of notes from a different scale. It can sound really cool when this happens.