Select of Type State

Help, need detailed and explicit instructions for a beginner
Use case:
1: select a country from a drop-down list
2. Select state from drop-down list if a specific country’s states are known.
3. Type in the state if specific country’s states are unknown.
4. State information is stored in same field, whether selected from drop-down list, or typed in.

Example data:
Country= “Country-1” “Country-2” “Country-3” “Country-4” “Country-5”
Country-1-states= “a” “b” “c” “d”
Country-2-states= “w” “x” “y” “z”
User will select States data from drop-down list for Country-1 and Country-2
User will type in States data for Country-3, Country-4, Country-5.