@ted202: Are you saying that during your PPL(A) theory you did not have flight planning and mass&balance lectures? Then during your training you did not do an Operational Flight Plan (+ ATC Flight plan mandatory if for example flying to controlled airspace) with mass&balance at least before each cross country flight (take off weight, fuel burn, landing weight) and a fuel calculation including reserve for your trip? Normally it have to be done even for aircraft with glass cockpit. You should also have an SOP of the school with some words about mass an balance in addition to what you find in the AFM.
If your school does not provide Operational Flight Plan that you can (or are obliged to in order to be allowed to fly) fill in with your calculations before each flight then what you have to do is use the AFM and read chapter 6 in the AFM for Cessna 152 (I did fly that one too and I believe the AFM should be similar) and if you got a complete AFM you will have an envelope there (figure 6-11) that you can make copies of and use to plot your Take off and landing weight, you will also find performance information in chapter 5 that you should understand and know how to calculate if you are going to fly to some foreign airfield to be able to prove to the examiner that you understand it and not just "its a long runway". And do not forget to check the documentation of the actual aircraft you are flying for the exam since every aircraft got different equipment and can have different basic empty weight its not like all C152 are the same, all C172 are the same, all C182 are the same etc.
@Pilot DAR: It may be fairly hard to load a Cessna wrong to get out of the envelope, but fairly easy done when taking passengers (during a time building or leisure flight for example) especially on Cessna 172 to overload it. Actually the only fatal accident in Poland of Cessna 172 (the pilot was experienced airline pilot still skipped m&b) because the aircraft was highly overloaded and unable to climb in a proper fashion from a difficult airfield when trying to avoid obstacles it hit the treetops and fell into a city park killing 2 of 4 occupants including the pilot. So mass and balance is important in every aircraft and in Cessna especially to not overload it. So no matter the aircraft doing the right thing is important....