Environments are set up in a way that contains your apps, forms, and info pages. Everything else, such as options sets, lookups, API Hosting, and Web/CDN Hosting, exists outside of environments.
They can be used to separate your development process by creating multiple environments such as development, testing, and production. For example, forms that are created in the development environment can be moved to the testing environment for user acceptance testing, and then finally released to the production environment.
Also, Environments can be used to separate specific projects, allowing for greater organization of apps, forms, and info pages in the CivicPlus Console.