PLC, I want to learn this, but people say I want to learn touch screen, frequency converter and server, but I don't have that much money.

PLC, touch screen and frequency converter can usually form a simple automatic control system. Touch screen is also called man-machine interface, through which users can set, monitor and control the parameters of PLC. PLC can control relays, contactors and frequency converters. You can buy some books on PLC for self-study. There are many kinds of industrial automation in bookstores, as long as you are not too stupid, you can do it! Step by step, as long as you are interested, it is your greatest motivation. If you can, you'd better study and practice, write your own program, input PLC, and actually run it to see if the action is the same as you expected. This thing is very important to practice. . . I hope it helps you.