How can a car battery be charged by dynamo (or is it an alternator?) at the same time it is being used by the car components?
In short, it can't. If the battery is being charged then current is flowing into it, so it can't be powering anything. It is the charger/dynamo/alternator that is powering the components whilst charging. In the case of a dynamo or alternator, if the output drops below the open-circuit terminal voltage of the battery, the battery takes over powering the components and is therefore no longer charging.