You can define environment variables for your resources, and they will be available in your application.
Preview Deployments could have different environment variables, so you can test your application as a staging environment for example.
Build Time Variables
If you would like to set environment variables for the build process, you can do by setting
Build Variable on the UI.
Developer / Normal View
You can see your enviroment variables in a developer view (like
.env) and in a normal view.
Developer view are useful to quickly overwrite or copy all your variables.