You have already had an answer to this when you posted it twenty minutes ago:
how to call class1.cs class on page[
^]
To reiterate Abhinav's response:
If you have created a class called class1 in you App_code folder, then in your page.cs all you have to do is declare an instance of class1 and use it as normal. Alternatively, as Abhinav said, you could declare static methods and properties and use those directly, just as you would with an other class.
Why is this giving you a problem?
Use the "Reply" feature below this answer to respond - do not create a new question.