The product page indicates which region or country the game can be activated in.
Products labelled as "Worldwide" region can be activated from any place in the world (unless otherwise indicated). Games tagged as "EU" can be activated only in Europe (including the UK), “UK” can only be activated in the United Kingdom, and "US" can only be activated in the United States.
Please make sure that the region of the game you are buying matches your region/country otherwise it will not work.