Don't worry, we've all been there. I agree with getting a handheld radio and listen to what goes on at your own airfield. Confidence grows steadily.
The basic A/G requirements are; Who are you? Where are you? What do you want? ATC will ask if there is any further information required. You have to learn what you are expected to respond to, but if you repeat the information given you won't go far wrong. Your Instructor will often prompt you as you may already have noticed (!)
If you visit an airfield with a higher level of radio service, or even full ATC, you may be given a printed aid to assist you.
Lastly, ATC are generally a helpful bunch and will know that you are in the early stages. Make sure that you have a kneeboard and pen ready to copy info. After a while the radio becomes second nature.
Have fun!