intake manifold

Took my car to the dealer and he had to replace the intake manifold. I know what it is, but I'm not exactly certain what the function is. Anyway, it was covered under my warranty, except for the fluids and oil filter. Does anyone know what fluids he would have to replace after installing the manifold and why he'd have to replace my oil filter?

To remove the intake you have to drain the coolant/Dexcool and its best to change the oil also after doing the work........~Larry~