Press your lips together to stop the air, then release. No vocal cord vibration.

Americans pronounce pm as pee-EHM (/ˌpiˈɛm/). Stress falls on the second syllable — keep everything else short and quick. You'll hear it in sentences like "We need to check in at the hotel before three p.m".
Record yourself saying "pm" and play it back. The mic stays on your device — nothing's uploaded.
2 syllables, 4 sounds. Tap a syllable to jump to its row, then explore each sound's mouth shape and how it's made.
The textbook way isn't wrong — it's just not how anyone actually says it.
Stress falls on the second syllable, not the others. Stretch EHM — keep everything else short and quick.