An environment is a collection of environment variables . A variable is a changeable value with a fixed name. Since your shell is a process like any other, it has an environment. You can view your shell's environment by entering the printenv command. On your system, the output will be different, but similar.
Environment variables are one way to configure the system.
Setting environment variables is simple. In order to show you the text one screenful at a time, man invokes a pager which shows you a new page of text each time you press the space bar. By default, it uses the pager called more . Go ahead and glance over the man page for less , which is an enhanced pager. After reading about the advantages of less , you might want to use it to read man pages.