How to charge my apple watch

Apple has instructions here.

Additional instructions are found in a support document called If your Apple Watch won't charge or it won't turn on

If you are asking about a charging brick, then you can use any USB-C port. The USB-C port can be on a personal computer, it can be the charging brick of a USB-C iPad, a USB-C iPhone, a USB-C Macbook Pro.

Or you can purchase a USB-C charger from any where (3rd party or Apple's). If you do decide to buy a USB-C charger, a 20watt charger will "Fast Charge" an Apple Watch Series 7.