What is a function call and how do I use it?

The function call is how you activate the JavaScript function on the HTML page. Without a function call, the JavaScript wouldn't know when to run or what to affect.

The function call goes into the HTML tag that activates the function. It must be paired with an "event", a type of trigger that will activate the function, such as the user clicking on it. For example, if you were using a button to change something on the page, the call would go in the button code like:
<input type="button" onclick="functionname()" value="click">