Press your lips together, add vocal cord vibration, then release.

Americans pronounce bagels as BAY-guhlz (/ˈbeɪgəlz/). Stress falls on the first syllable — keep everything else short and quick.
Record yourself saying "bagels" and play it back. The mic stays on your device — nothing's uploaded.
2 syllables, 6 sounds. Tap a syllable to jump to its row, then explore each sound's mouth shape and how it's made.
Raise the back of your tongue to touch the soft palate. Add vocal cord vibration, then release.

Relax your lips, jaw, and tongue completely. Drop your jaw slightly and keep the tongue neutral.
Keep the tongue tip down and pull the back of the tongue up toward the throat. The 'dark' sound comes from the back.

Same position as S, but add vocal cord vibration. Feel the buzz.

The textbook way isn't wrong — it's just not how anyone actually says it.
Stress falls on the first syllable, not the others. Stretch BAY — keep everything else short and quick.
Don't pronounce the first syllable too fully. The unstressed syllable reduces to a schwa — the lazy "uh" sound — in casual speech.