Here for example is a piece made up largely of the harmonics (Portrait of Tracy Jaco Pastorius) https://www.youtube.com/watch?v=nsZ_1mPOuyk That's an electric bass and the bell-like sounds are harmonics. Basically he's just lightly touching the string in specific places to suppress the fundamental tone so you just hear the harmonics.

Whereas here (Stir it up - Bob Marley and the Wailers) https://www.youtube.com/watch?v=1hwL3S3Gtzs when the bass comes in, the player is holding his hand near the bridge (back of the strings) with the side of the palm resting on the strings to suppress all the harmonics so you only get the fundamental tone and it has this sort of muffled quality (because a lot of the brightness comes from harmonics).