The book makes understanding variables quite easy.  We’ll add a little here:

Most languages have a way to define constants.  A constant is a value that cannot be changed.

In some languages, constants are variables that are not allowed to be changed.

In some languages, constants are variables that should not be changed.

In some languages, constants look like variables, but are really just values that are used by the compiler or interpreter.

JavaScript does not have a way to define or use constants!

Many languages require that the  type of the variable be defined.  For instance, in Java you might define:
            int x;
Which means to define a variable called x and to specify that it will contain an integer.  These languages are “strongly typed”.  JavaScript is not “typed”, because:
            var x;
Can contain an integer, a floating point value, a string, or anything you like.

Likewise, the book does a good job on functions, but here’s a little more info:

Many languages, especially “strongly typed” languages, make a distinction between functions and subroutines.

A function returns a value of a certain type

A subroutine does not return a value (in other words, it’s a function that does not return a value)

Since JavaScript is not a “strongly typed” language, there is no reason to make a distinction between functions that return a value and those that don’t.

Using only the techniques from modules one and two, and chapters one through four of the textbook:

Create two files, one named second.html and the other named second.js

Write code to create a web page that uses a JavaScript program to output a NASA style count down:

            Ten
            Nine
            …
            One
            Ignition Start
            Liftoff
            We have Liftoff!

Each line must be displayed as an alert

Create a generic function that outputs one line of the countdown as an alert, and receives the data to output as an input parameter.

Use that function to output each line of the countdown.

Each line, after the first line, must only be output when the user clicks “Ok” in response to the alert.

Use comments and lay the code out so it can be easily followed!

Each file in the assignment must have a comment at the top, using the correct commenting technique for the file type, like this:
            Your Name
            Your Student ID
            CST140
            Assignment 2

Test your program by opening the web page in your browser. You should see the NASA countdown displayed as a series of alerts (which are displayed one at a time in a popup window.) Click the OK button to display the next line in the countdown.
No text is required to be written directly to the browser window.

Create a countdown 
Create two files, one named second.html and the other named second.js
Write code to create a web page that uses a JavaScript program to output a NASA style count down: Ten…Nine…One…Ignition Start Lift-off We have Lift-off!
Each line must be displayed as an alert
Create a generic function that outputs one line of the countdown as an alert, and receives the data to output as an input parameter.
Use that function to output each line of the countdown.
Each line, after the first line, must only be output when the user clicks “Ok” in response to the alert. 
(see more specific instruction in attached document)