For the 172M, after about a three second Google search, I found this:
http://www.hva.com.au/Uploads/Cessna...odel%20POH.pdf
Download it and read through. Sure, some of it may not be clear to you now, but by the time you earn your PPL, everything in this manual should make sense to you. Your instructor should be able to easily explain everything which is presented in this manual. Legally, this manual must be carried aboard the aircraft during flight. It costs nothing to sit in an aircraft which is not running, so pick a poor weather day, sit in the plane (and walk around it) with the manual in your hands, and equate everything - the manual explains it all.
Probably in your national regulations, there is one somewhere (which in all fairness, you would not yet have been introduced to) which will read something like "The pilot shall operate the aircraft in accordance with the manufacturer's manuals and checklists, and within its limitations". The flight manual/pilot operating handbook from the aircraft manufacturer is the document you refer to to comply with that regulation. If you do not refer to the flight manual, and it's checklists, and something goes wrong, an authoritative person may be asking you why you were not complying with the manufacturer's procedures and limitations. I would not like to have to answer that question myself!
Also note, that probably of little affect on the 172M you fly, there still may be approved flight manual supplements associated with modifications done to that particular plane. You would also be responsible for knowing and operating within those. Just reading only the flight manual is not enough. An example is that some modifications impose speed limitations which you would like to know about! During an approval process, I once limited a 172M with a photo door installed to a never exceed speed of 125 knots. This was because I found during testing that at 135 knots, the door shook so badly I thought I would loose it! So, there's an approved flight manual supplement for that photo door, and requirement to placard the airspeed indicator when it's installed, which I wrote. Woe be the pilot who disregards, and flies it faster than 135 knots!
Beyond the manual, I highly recommend the book "Cessna, Wings for the World" by Thompson. He was a Cessna test pilot, and explains everything about the whole single engine series. It is certain that if you read the section of that book about 172's, you will know more than your instructor about the development history of the plane, and why things are the way they are - it's fascinating.