Question

What should a computer science freshman do in summers other than interning?

Answer 1

As a freshman, the best thing you could do is 'Build and Learn' process.
This is the best process to repeat continuously, in order to get a great knowledge of computer science.

Just choose a project that you gonna build and then start building it. Keep one thing in your mind! Building a project includes the learning and exploring part also.

As a noob, just create some basic things like calculator using HTML, CSS and JavaScript.

I don't know what you mean by freshman! Did you mean someone new to computer science or someone who just graduated? Let me know because, I answered this with assumption that you're new to computer science.