If my screen is black on my Apple watch what do I got to do get it to come on

See this and if nothing helps, the last step in the article has a link to contact Apple Support --> If your Apple Watch won't charge or it won't turn on - Apple Support

Click the words in blue, which is a link to an Apple Support Article, which gives you suggestions on things to try if your watch won't turn on or charge. And if after doing the things in the linked article aren't successful, then contact Apple Support.