An environment variable is a dynamic "object" on a computer, containing an editable value, which may be used by one or more software programs in Windows. Environment variables help programs know what directory to install files in, where to store temporary files, and where to find user profile settings. They help shape the environment that the programs on your computer use to run.
The variable name shown in the picture, %appdata%, is one of the environment variables used by Microsoft Windows. It points to the application data folder, where many programs store data specific to your user. Its value is the name of a directory. Like any directory name, you can open it in a File Explorer window by entering it in the Windows Run box or Windows Search Box. For example, to get into the Application Data folder type %appdata% and then press Enter in the Run box. This variable is one example of how environment variables can make your life a little more convenient.
From the Windows command line, you can the set command to view all Windows environment variables, and their current values.