The dev environment is a separate workspace where you can make changes and preview them locally, instead of doing a build → push step every time.
If you want those changes to show in your live workspace (i.e. not Preview workspace) you need to do the embeddable:build + embeddable:push steps.
When you first create your dev workspace it will be automatically connected to our sample database. Pop us a message to get it hooked up to your database 
Note: currently build+push doesn’t work if you have the dev running. You need to stop dev first, then build and push. A fix for this is coming soon!