Baby in car seat

Those that have vehicle, either yours or family car, and owns a baby. Im a first time mum and would like opinions. Do you always put your baby in car seat or sometimes you also carry them in the car? Assuming baby is 6 months and lesser, or newborn. Example if the car needs more people in it, do you remove your carseat and just hold the baby or do you still use baby seat in the rear seat? #firsttimemom