Just to take it a little bit farther.

The root, 3rd, and 5th. Can be called degrees of the scale also. 5th degree of the scale, 3rd degree of the scale and so on.

It's hard to explain, but all chords come from scale structure. for example a root, flattened 3rd and a 5th make a minor chord. and so on.

I've tried to explain, and Christoph did a good job.