my new apple watch(just out of the box) gets warm but will not charge

Please refer to the steps listed in If your Apple Watch won't charge or it won't turn on - Apple Support. After reviewing the information provided, without resolution, be sure to use the "Contact Apple Support" link listed under "Learn More."

Have you paired the watch with your phone or tried to set up?

See this link --> Set up and pair your Apple Watch with iPhone - Apple Support