I am not understanding the second part of the Random Number Challenge.

//create a variable and initialize it to the value provided by the user via the prompt
//E.g., if the user enters 23 then the value of input1 will be "23"
var input1 = prompt("Please type a starting number");

//convert the user input's to a number using parseInt(), and store it in a variable named bottomNumber
//prompts return Strings, so the input has to be converted to a number: 23
var bottomNumber = parseInt(input1);

//create a 2nd variable and initialize it to the value provided by the user via the prompt
//E.g., if the user enters 101 then the value of input will be "101"
var input = prompt("Please type an ending number");

//convert user input to number and store in topNumber
//after this step topNumber will be a number: 101
var topNumber = parseInt(input);

//generate a random number between topNumber and bottom Number using the 
//Math.floor() and Math.random() methods, and the formula (max - min + 1) + min
//So the variable randomNumber will be Math.floor(Math.random() * (101 - 23 + 1) + 23)
var randomNumber = Math.floor(Math.random() * (topNumber - bottomNumber + 1) + bottomNumber);

//create a String using concatenation (+) to put it all together into one message
var message = "<p>" + randomNumber + " is a number between " + bottomNumber + " and " + topNumber + ".</p>";

//write the message to the page
document.write(message);