Why is my printer is not printing my doents on my computer?

Ok I have homework that I receive from my email online and blackboard, and everytime I try to print it out, the paper does goes through, but the ink does not come on the page, its like its printing out blank ink. Then when my mom test to see if it is the ink on the internet, it either prints out certain words or print the page of words and pictures in multicolor ink. Its it something wrong with the ink or the printer itself, because it prints, its just the ink or the words on the page is not showing?