Select data field to display in dropdownlist (Id Control)

Question

hi guys

i have 2 tbls are below

1/(RegionTbl).

Region id PK

RegionName Nvarchar

2/ (CityTbl)

CityID

RegionID Fk

CityName Nvarchar Pk

and in application i have 2 dropdownlist , list1 is datasource from RegionTble To select RegionName and list 2 from CityName in order to seletc from list1 regionname to display cities in list2 as afilter data

please give me solution step by step