Press your lips together. Air flows through your nose. Vocal cords vibrate.

Americans pronounce marathon as MEH-ruh-thahn (/ˈmɛrəˌθɑn/). Stress falls on the first syllable — keep everything else short and quick. You'll hear it in sentences like "The marathon route goes through the city center" or "She is training for a marathon and runs twenty miles a week" — more examples below.
Record yourself saying "marathon" and play it back. The mic stays on your device — nothing's uploaded.
3 syllables, 7 sounds. Tap a syllable to jump to its row, then explore each sound's mouth shape and how it's made.
Place the very tip of your tongue slightly between your teeth. Blow air gently around it without voicing.

Relax your lips and drop your jaw significantly. The tongue tip lightly touches behind the bottom front teeth and the back part of the tongue presses down a little to create more dark space in the back of the mouth.

Touch the tip or front edge of your tongue to the roof of your mouth behind your teeth. Air flows through your nose.

Click any sentence to see the full breakdown — every link, every reduction, every flap-T.
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 MEH — 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.