Complex sentence: The "Global Passport Power Rank" ranks passports by their visa-free score (VFS), which is the number of countries a nation's passport-holder can visit visa-free (VF) or by obtaining a visa on arrival (VOA).
Split into simpler sentences: The "Global Passport Power Rank" ranks passports by their visa-free score, which is the number of countries a nation's passport-holder can visit visa-free or by obtaining a visa on arrival. First, it adds up the number of countries a nation's passport-holder can without a travel visa or by obtaining a visa on arrival (VOA).