This is not so much a tutorial as its a code snippet with example.

/** 
* Generate a random number
* @return Random Number
* @error throws Error if low or high is not provided
*/  
function randomNumber(low:Number=NaN, high:Number=NaN):Number
{
  var low:Number = low;
  var high:Number = high;

  if(isNaN(low))
  {
    throw new Error("low must be defined");
  }
  if(isNaN(high))
  {
    throw new Error("high must be defined");
  }

  return Math.round(Math.random() * (high - low)) + low;
}

Here is how to call the function, just a simple usage.. this can be used for any number of things. Pass in an array length, age range or coordinates.. its up to you

trace("Random Number : " +randomNumber(3, 10));