RSlogix 5000 Level Control

Hello, I'm currently working on a program that requires a PID instruction to keep the level at a set point.

Hardware:

Solenoid valve (Relay output)
Control Valve ( Analog 4-20 mA output)
ultrasonic Sensor ( Analog 4- 20 mA input)
Differential Level Meter (Analog 4-20 mA input)
Flow meter ( Analog 4 - 20 mA input)
VFD ( connected to digital output and connected to analog output for a 4-20 mA speed reference)

PLC processor 1769-L32E with Digital I/O - 1769-IQ6XOW4, Analog I/O - 1769-IF4XOF21 and Relay Output - 1769-OW16.

I already configured my I/O on Rslogix 5000 but i am confused on how to start to write this program. Any ideas how?

First at all, you need a philosophy of operation. So:

a) Ask for that document to your boss/client/production guy.
b) If the document does not exist, take paper and pencil and start writing it.

When the document will be ready you can start writing a program.

And welcome to the forum.