Conditional formula query (drop down lists)

Hi, first time on any of these forums.
I have an excel spreadsheet that has two lists. After selecting from the first list, I want the second list to be restricted based on what has been chosen from the first list.
Eg first list contains list of countries. Second list contains list of cities. Therefore if I chose England from the first drop down list, how do ensure the second drop down list then is restricted to just English cities - is there a special formula function I can use?
Thanks.

Have a look here: Dependent lists