The Spanish letter o has a pronunciation similar to that of the "long 'o'" sound of English, although purer and perhaps a bit shorter in duration.
In English, it is common when pronouncing the "o" to pronounce a blend of the "oh" sound followed by an "oo" (the sound in "boot"), so that the word "oh" can sound something like "oh-oo." In Spanish, however, the "oo" sound is absent. Otherwise, the sound of the Spanish o is one that is very familiar to English speakers.
Spanish o is never pronounced like the "o" in "love" or the "o" in "prove."
Phrases used in the accompanying audio lesson on pronouncing the o are "¿Cómo no?" ("Of course" or "Why not?" as a means of expressing agreement) and "Lo siento mucho" (I'm very sorry).