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

Americans pronounce plunge as PLUHNJ (/plʌndʒ/). It's 5 sounds in 1 syllable. Every consonant in the cluster gets its turn — no shortcuts in casual American speech.
Record yourself saying "plunge" and play it back. The mic stays on your device — nothing's uploaded.
1 syllable, 5 sounds. Explore each sound's mouth shape and how it's made.
Press your lips together to stop the air, then release. No vocal cord vibration.

Place the tip of your tongue against the alveolar ridge just behind your top front teeth, the same contact point as /t/, /d/, and /n/. The difference is what happens to the air: for /l/, you let it flow continuously around the <em>sides</em> of the tongue (that's why /l/ is called a lateral). Turn your voice on the whole time. Lips stay relaxed, no rounding or flaring. For the Dark L variant at the end of a syllable, also pull the back of the tongue up and back toward the soft palate.

Relax your lips, jaw, and tongue completely. Drop your jaw slightly and keep the tongue neutral.
Touch the tip or front edge of your tongue to the roof of your mouth behind your teeth. Air flows through your nose.

Touch the front of your tongue to the roof of your mouth, then release into a 'zh' position. Add vocal cord vibration.
