An apostille is an authentication document certifying the validity of public documents for use in other countries or jurisdictions. They are issued in the jurisdictions where the document to which they refer was issued.
When making Aliyah it is required on most public documents (Marriage, Divorce and Death Certificates for example) issued after 1988.
Countries which are not signatories to the Hague Convention are not able to issue Apostilles. A different documentation verification process will be required. Your local Aliyah office will be able to give you details. Of the main English speaking countries, only Canada is not able to issue an Apostille.