How to play "Chord Harmonies" on guitar

Now that we built a riff, we can start adding to it to make our composition sound more full. One of the things we can do, especially in metal because of the standard practice of having two guitarists, is use chord harmonies. Basically what this is is playing two chords at the same time. Doing this fills in more gaps and flushes out your story by directing the listener towards a certain emotional feeling due to the happiness, sadness, or dissonance of the chord harmonies.