Environments are the contexts or stages of the project such as Dev, QA, Staging or Production. Initially, you have a Default environment created and it is named as default environment. Every environment carries its own user base.
In the Dashboard sidebar, you can see the current Project, environment, and dimension. From the sidebar dropdown, you can easily switch environments.
If you want to create a new environment, click on the create icon. Give the environment name accordingly and make sure that the environment key value is unique throughout the project. You cannot modify the environment key after it is created, but the environment name can be modified at any time.