what does the length of the smallintestine relate to his function in absorbing digested food.?

Answer 1

The length of the small intestine along with the many levels of folds and villi which are covered in microvilli all serve to increase the absorptive area.

If due to surgery, someone loses a significant portion of their small bowel they can suffer from a "short bowel syndrome" which means they lack sufficient absorptive capability to remain healthy.

Answer 2

Because the small intestine is relatively long, food spends more time passing through it, so there is more time for the body to absorb the digested food.