https://www.cnet.com/news/app-store-could-be-coming-to-watchos-at-wwdc-report-says/

Current Apple Watch apps need to be downloaded through the iPhone's Watch app and then transferred over to the Watch. 

It's unclear when Apple might release the new update to the public. The company has traditionally first detailed major software changes at the June event before releasing them to the public, often alongside updated hardware, in the fall.