Apostille is done for personal documents like birth/death/marriage certificates, Affidavits, Power of Attorney, etc. and educational documents like degree, diploma, matriculation and secondary level certificates etc.
Apostille is acceptable in 105 member-countries of the Hague Convention. So that means! Once you get a document apostilled, it will be recognised by the below 105 countries Thus, greatly simplifying the process of attestation by making it needless to get the documents attested in each or for each of the countries separately.
The Hague Conference has currently 82 Members: 81 States and 1 Regional Economic Integration Organisation. For the dates of membership, please consult the status table of the Statute of the Hague Conference.