There are two types of environment variables on Forest.host.
First there are System variables. These are provided by services defined in blueprints or provided by Forest.host. For example: database credentials are provided by the database services and exposed as environment variables.
Environment variables are just what you expect: variables available in the running environment.
You can add environment variables as you like. They will be available after a deploy. If you’re service is already running, either use redeploy or trigger a new build.