I believe a propper way to indicate this would be as such: "I trained multiple people in/to <topic/activity> during my time at <location>."

I trained 50 people in Computer Science. I provided training for 50 people in the area of Computer Science. I assisted in providing training for 50 people in the area of Computer Science. I assisted in the training of 50 individuals in the area of Computer Science. There are many ways to state this - these are just a few. Hope it helps :)

Trainee, possibly undertakes a technology transfer before going on a professional skills, so as to pass on to a new junior employee who is just graduated or employed in a current year, usually can win lower salary than the other senior employees, staying in a company for more than 3 or 5 years. And trainer,is the senior employees who can teach or guide trainees to approach their sophisticated techniques in a company before formally accepted or employed by your boss, also the salary ought to be higher than other common employees.