The first few lines create variables (title, genre, and year) to hold the values from the text boxes. The line if(IsPost) makes sure that the variables are set only when users click the Add Movie button — that is, when the form has been posted.
As you saw in an earlier tutorial, you get the value of a text box by using an expression like Request.Form["name"], where name is the name of the element.
The names of the variables (title, genre, and year) are arbitrary. Like the names that you assign to elements, you can call them anything you like. (The names of the variables don't have to match the name attributes of elements on the form.) But as with the elements, it's a good idea to use variable names that reflect the data that they contain. When you write code, consistent names make it easier for you to remember what data you're working with.