For each tripoint, you have to type the first three letters of the three countries in any order (eg ITAFRAGER would work for hypothetical France-Germany-Italy tripoint). For 4 countries you type the acronym instead of the first letters (see notes for the list)
Data from http://en.wikipedia.org/wiki/List_of_tripoints; country names from 'Countries of the World Quiz'
Countries in tripoints listed in alphabetical order, tripoints listed in alphabetical order
Exceptions: CAR for Central African Republic, DRC for Democratic Republic of the Congo, RoC for Republic of the Congo, UAE for United Arab Emirates
As a hint you are shown the first letter of the first country; these are grouped together when the first country is the same