You are always going to have some sensation in your body, for example, the feeling of your behind touching the cushion or chair. The main idea is to notice that the sensations go away or change. The "insight" part of it connects to the "triple gem":
1. Annicca ( impermanence )
2. Anatta ( nobody and no thing has an "essence" or a "self" )
3. Dukha ( unsatisfactory feelings ranging from unsatisfactory -> suffering )
Buddhists believe that these are 3 root truths of life and that if a person learns to see these 3 things all over life, for him, herself that s/he will be "liberated" from "dukha" ( suffering ).
The idea behind vipassana bhavanna ( insight meditation ) is to train you to see things in these terms.
In reading the scriptures, there are two kinds of mistakes:
One mistake is to cling to the literal text and miss the inner principles.
The second mistake is to recognize the principles but not apply them to your own mind, so that you waste time and just make them into causes of entanglement.