Hi Mohamed, You are very welcome! The input and output devices will be connected to the PLC input and output cards and that's how you'll be able to access these devices via your PLC program and tell them what do to.
We have a two-part video series on this topic on YouTube. You can watch them via the links below.
How Are Field Devices Wired to PLCs? - Part 1
How Are Field Devices Wired to PLCs? - Part 2