How am I supposed to behave in a Shiva (שבעה)

I am not very religious, and fortunately for me I haven't experienced the death of a loved one ever since early childhood, before I could understand it.

Now, I wasn't able to visit the friend's funeral and I want to attend his Shiva, but I am not fully sure how to behave, what to do. The friend comes from a religious home close to Jerusalem and it is close to the end of the Shiva. Is there anyone who might help me better understand if there is anything I should do or not do?