What does the piece next to the radiator do?

air ducts to help the vehicle's radiator and engine cool down

If the air is going to breathe, why is the floor in front of those covers closed with plastic parts?

perhaps it was later left to connect a part or accessory

I guess to prevent dirt from entering with the blowing wind when it stops. I think it opens with a certain wind force.

vehicle chassis are being produced the same, possibly in diesel or diesel, there is another engine part or it may have been left for easier intervention