New to PLC's

I am currently learning through online courses and internet about PLC's and there functions.

I have been asked with regards to field devices, what are they and examples?

Am i getting confused with I/O's switches relays extra or are the two completly different.

Thanks in advance

Welcome to the forum.
Field devices are simply the things wired to the PLC. PLC inputs are the devices whose signals are required to make the control choices. PLC outputs are the devices controlled by the PLC program.
Before you can effectively program a PLC you need to understand how the field devices function.

PLCs are typically used to control outputs based on some inputs.
A basic example of this would be a start and stop button would be connected to the PLC inputs, and the PLC program starts an internal timer and after 5 seconds the PLC output switches on, which energises a contactor to start a motor.

Anything connected to the PLC control system in one way or another that is external to the PLC control panel is what I would refer to as a field device, that could be anything from pushbuttons, sensors, remote IO to motors and valves.

I guess you're totally new to the industry, you're best bet is to start with learning what happens externally to the PLC, then if you know what happens externally, then you know what needs to happen internally to the PLC (i.e. the program). Start with an electrical engineering course or youtube for electrical engineering basics and that will help get you started