Most of the books about Middle Ages are in the 940.1 section of the Non-fiction shelves.
There is a lot of material available on the Internet therefore it is important to use effective search techniques to find the right material to suit your needs.
You must first decide on your Search terms.
For example, try Medieval life - Middle Ages.
Or be more specific: The Plague, The Black Death, Castles, Monks and Monasteries, Monarchs, Peasants, Knights, Lords.
Make sure you use this fantastic ebook.
Living in the Middle Ages is a great ebook that covers most of the topics you are needing to research for your studies on the Middle Ages.
Knight by 
Castle by 
Life on a Medieval Manor by 
Monks and Monasteries in the Middle Ages by 
Eyewitness Medieval Life by Click on these web-sites for information about Medieval Life