Your birth certificate is the official document that authenticates your existence and birth. It registers your nationality and familial lineage. The information there is recognized by the government and therefore honored everywhere to prove your identity. Only the government can give you an authenticated copy.
With the computerization of government agencies and offices, obtaining copies of birth certificates have become easier. It has become more convenient, too, with the online ordering and payment scheme. If you have moved to another state, this is good news for you.
Birth certificates are official government documents. Copies therefore need to be authenticated first before it can be honored, especially when used to prove identities in major official transactions. Simply photocopying the certificate will not suffice. Only the city hall or municipal office where you birth was registered is authorized to produce an official copy from the original (and only they keep the original). A seal authenticates the document. Forging your birth certificate is strictly prohibited as it is equal to tampering a government registered document, and consequently a government seal. You may, of course, still keep a photocopy for your file or which you can use for minor transactions where an authenticated copy is required.
Parents, when they file for a birth certificate of their child are given an authenticated copy of the document. Institutions like schools and hospitals will require to be provided with an authenticated copy for their file. If you are a parent, be sure you take care of that copy; otherwise, you will need to obtain another one from city hall or municipal office where your child is registered. Obtaining a copy is not free. You will be charged a fee, plus tax. Of course, you will also need to prove first that you are the legal parents when you request for a copy.