How do I charge my watch

The package holding a new watch comes with a little disk, about the size of the watch, with an indentation on one side that allows it to fit snugly against the back of the watch. There are no wires or contacts between the disk and the watch, so the watch has not holes in it that would allow corrosion. The disk has a wire with a USB connector that can plug into a USB power adapter. Some charger cables have USB-A, some USB-c. You can see pictures at the link that Vancouver22 referred to.

See: Check your battery and charge your Apple Watch

You will need a 20W USB-C Power Adapter (not included in the box)