A shell variable is local to the current shell session and it cannot be accessed by other shells or processes, you will set it usually by my_var=value and of course without "export".
Shell variables are usually used to store temporary values or to restrict the scope only to the local shell session so it can not be shared outside of it .
An environment variable on the hand is accessible by the shell and the processes it spawns. In unix-like systems environment variables are typically capitalized by convention. to declare env variables or to make a shell variable an environment variable, you need to use the "export" command: export MY_VAR="Hello!"
PATH for example is a common environment variable.
when you set an environment variable in a terminal session, it will only last as long as that session remains open and to make it persist across sessions, you need to define it in shell config file like .bashrc if you use bash as your shell.
to display a shell variable you will use echo command :
echo $my_var
