What is attestation?
The attestation is the method of checking the authenticity of a document & declaring its authenticity by attaching it with the sign of the verifying personnel. The process requires the submission of original documents as well as a xerox of the same to authorized employees for verifying and required sign/stamp on the guided area.
If you want to travel to another country you will need to apply for a visa and as a matter of fact, the visa will be issued only when officials have verified your documents thus this make attestation of required documents necessary. Similarly, if you are looking for a family visa then attestation of the marriage certificate attestation is mandatory.