The interviewer knows that you don't have any experience, so he's not expecting you to.
What he'll be looking for, is to see that you're smart, reliable, that you communicate well, that you use your initiative etc.
In order to make an impression - engage with him - answer his questions.
IT interviews typically involve some technical questions, so it's good to be able to answer them. For example, you should be able to say what the difference of between a linked list and an array is, and the advantages of each.
They might give you a problem solving exercise, even if you can't solve it, they're wanting to see how you go about solving these problems, and how well you communicate through it.
Remember, they're looking for not just technical skills, but your interpersonal skills as well. All the technical skills in the world aren't going to help if you're difficult to get along with or are unable to communicate.