This is the 5261st most frequent Turkish word.
kamyonu
"The truck" (in accusative case).
Here, 'kamyonu' is the accusative form of the word 'kamyon' ('truck'), showing that it is the direct object of the verb 'park ettik' (we parked).
Kamyonu yola park ettik.
We parked the truck on the road.
In this sentence, 'kamyonu' remains in the accusative form and acts as the direct object of the verb 'sürerken' (while driving).
Çocuk, kamyonu sürerken dikkatli olmalı.
The child should be careful while driving the truck.
Here again, 'kamyonu' is in the accusative case, as it is being specifically referenced by the verb 'gördüğümde' (when I saw).