How to set Global Variables?

Unfortunately, you do happen to be incorrect.  The "temporary" designation for temporary project variables has to do with whether or not the value of the variable persists between test runs. So, you have a project... while running the project, you set the value of the variable.  So long as the project is running, that value persists unless it is changed.  When the project stops running, the value is cleared and the variable is reset to default.  

Think of it as such:

var tempVariable = 'default';

function test1() {
    Log.Message(tempVariable);
    tempVariable = 'my test';
    Log.Message(tempVariable);
}

function test2(){
    Log.Message(tempVariable);

}


function foo() {
    test1();
    test2();
}

When you run function foo, the output should show in the log as

default <- The log message before the variable value is set

my test <- The log message in test1 after the variable value is set

my test <- The log message in test2

If you rerun function foo, you'll get the same output.

Think of "foo" as your project and "tempVariable" as your temporary project variable.