Euro is a common currency in about 19 countries in the European Union of 28countries. Eurozone is the area of those countries where Euro is valid-now 19 countries. Alphabetically writing these coutries are: Austria,Belgium, Cyprus, Estonia, Finland France ,Germany, Greece, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Portugal, Slovakia, Slovenia and Spain.
The initial countries were only 12 in 2002 and the last country joined as late as 2015.
As of now the notable countries not in Eurozone (not using Euro)are United Kingdom,Denmark,Poland, Hungary, Sweden etc.
As per the arrangement debit cards and credit cards issued by one of th Eurozone countries can be easily used within other Eurozone countries .