You must either send CMS original copies of requested documentation, CMS will then copy and certify the documents as true copies and either return the original or store the original in a safe place for you to collect them when you enter Australia or ensure you forward to CMS certified copies of all requested documents.
Typically certification is required for:

• Passports
• Birth certificates
• Marriage certificates
• Death certificates
• Copies of qualifications
• Copies of employment references

To have documentation certified you need to take your original transcripts / documents and a copy of each transcript to an authorised person in your community.
Authorised persons include Justices of the Peace, Notary Publics, lawyers / solicitors, Magistrates offices and (in some countries only - Police Officers and School Teachers or University professors.
They need to sign on your copies that they are true and correct, print their name and position and if possible affix an official stamp