Using Environment Variables in Flows

I have defined environment variables, which I would like to use in a Flow. I have two questions:

  1. How can I access environment variables in an Evaluate block?

  2. How can I make sure the environment variables of the current environment (i.e. selected in the upper right corner of the Postman window) are used in Send Request Blocks (i.e. without having to select the environment in the Send Request blocks).

Hints for either question are appreciated. Many thanks.