How do I make node-red "talk" to the pre-existing hardware?

Hi everyone,
My question may sound quite basic to many of you, but my background is in manufacturing/operations and I am new to node-red.
I want to develop an application for temperature monitoring and control for small factories using node red. The app must be able to communicate with pre-existing hardware, as most producers already have installed hardware/sensors to monitor temperature data.
So my question is: how do I make node red "talk" to the pre-existing hardware?

Thank you

I'm afraid you're gonna get little to no help without specific information.

There are thousands of sensors, PLCs, applications each with their own protocols.

We simply cannot provide information on them all.

Why don't you start with what you have tried, what devices you wish to communicate with, what protocols they use etc.

As Steve says, you firstly need to understand how anything can talk to the hardware.

Is it network enabled? If so, does it support MQTT or some other messaging broker type?

Or does it have a serial/USB interface? Or even GPIO?

Are interfaces documented? Are they open or proprietary?

Even giving us a clue as to what type of hardware would give us a starting point to help.

Node-RED can talk to most hardware that has an interface of some sorts.