To help with understanding what you hear, you might consider getting an airband receiver and listening as often as possible to ATC at an airfield (preferably your own) which handles light aircraft. (It is not much use listening to Heathrow Approach as they just don't say the same things!)
Don't just put it on in the background but try to copy down the relevant points as if you were going to read it back. If possible connect a headset to it to increase the realism. You will start to become familiar with the standard phrases at that airfield eg. there are only a limited number of ways you can make a circuit join and ATC will usually use almost exactly the same phrases to describe each one.
Before you start speaking on the radio write down either all of what you need to say or at least an aide-memoire (mine was CARPAR but your instructor will have his/her own) and look at it while you are speaking.
Also before you speak, think about what information you are going to get back - is it going to be a takeoff clearance with a turn direction, is it going to be a landing clearance (easy to answer that one) or is it going to be something like 'Next call turning base" and be ready to filter out the actual numbers and instructions.
Definitely don't become disheartened - it WILL get better!
Just another thought - if you can arrange a visit to the tower through your flying school that will help - you get to find out that ATC actually have arms and legs and heads like the rest of us!