Where do I plug my earphones on IPhone8?

"What's the box" includes:

"Lightning to 3.5 mm Headphone Jack Adapter"

you will need either bluetooth or lighting cables.

if you have a set of headphones with a 1/8" or 1/4" jack you will need a 3rd party adapter from whatever size you are using to lightning adapter.

The iPhone 8 does not have a traditional ring/plug headphone jack.

Headphones - iPhone 8 - Headphones & Speakers - iPhone Accessories - Apple