What are the side effects of advil?

I have been feeling severe pain in my body, joints and head. Even taking Aspirin did not help as I was having high fever that was taking a toll on me and my work. My whole body seemed to have terrible ache that was difficult to subside. Then my brother gave me a bottle of Advil and told me to take only two tablets which will give me immediate relief. I want to know before taking Advil that what are the side effects it can cause?