Control flow is the order in which lines of code are performed. Code is performed from the top of the document to the bottom until that flow is changed by something such as a conditional statement or loop.
A function in JavaScript is a block of code which performs a specific action and is reusable. A function is used by calling, or invoking, it by using the following syntax:
myFunction()
The parenthesis after the function name is used to provide data to the function which can be then be used by that function to perform an action or series of actions with said data. For example:
alert("Hello!") //Creates dialog box with the text "Hello!"