I found a great link for a list of script calls which I will share here: RMMV Script Calls.
Below is the call I was looking for.
Where you see the abbreviation "var" you put the number of the variable you wish to store the text (or string). Then where you see "value" is where you place the text. Make sure you put quotation marks around the text in the "value" part or it will run an error.
So it should read something like:
$gameVariables.setValue(1, "Hello World");
Using the variable hasn't changed, thankfully.