First, verify that you are inside the workflow directory: 
$ ls

Dockerfile      reference       wf      version
Then, use latch preview and pass in the current working directory: 
$ latch preview .
This will open up a preview in the browser automatically. If after using latch preview, this does not open automatically, navigate to Latch Console. In the Workflows section, a new button with the workflow name will appear on the top right corner. You can click on this button to preview the interface. Screenshot of the workflow interface preview page