There are 9 effective planets are there.
There are 12 sun signs / rasi / houses which are allocated to these motionary planet as each house will have a primary allocation of a planet which is called as ruling planet for that particular house.
As each sun sign is having a assigned ruling planet, the properties of the ruling planet affects the respective house. Additionally, as each planet's actual position varies from time to time based on its transition duration in each house, each sun sign house get to happen to have either no planet or one planet or multiple planets at a time. So the present planetary position in each house will give their effects on the house according to the plnetary properties which also dependent on their relationship with the native planet of that particular house.