GTA training is essentially being shown first then demonstrating the exam techniques with a senior GTA as trainer. In my case, there were three of us newbies and the trainer, all of us in gowns. Each section of the exam was demonstrated by the trainer, then each of us would do the same.
While each center has their own standards and idiosyncrasies, the basics are:
Students enter the exam room to find the GTA in the gown with a sheet over lap and legs, on the exam table.
After an introduction and explanation of the process, the GTA will begin the demo. I change my presentation depending on what kind of students they are. Nurse practitioners, for example, don't need instructions on hand washing and draping, 2nd year med students do.
The exam is shown systematically. First is the examination of the pubic hair, supra pubic area and inguinal lymph nodes.
After that, the exam of the penis and testicles is shown.
Each student practices those techniques.
Next the GTA stands for the hernia exam. Each student practices.
Last is the rectal/prostate exam. Where I work, we teach the exam standing, bent over the table. After explaining the process using a fist as a demo anus, each student practices.
All through the process, the students are guided and corrected as necessary.