How can I learn how to make a 7th chord?

To learn how to make a 7th chord, you need to understand the basic structure of chords and how to add the 7th note to them. Start by learning the major and minor chords, then add the 7th note which is a whole step below the root note of the chord. Practice playing and listening to different 7th chords to become familiar with their sound and how they are constructed.