what are the differences if we get it online or by mail?
There are no differences between a driving record you order online or by mail.  They are all certified DMV records. They all include a certification statement and the signature of the Commissioner of Motor Vehicles, as well as the same security watermark.
no that is not what I meant. can I ask something else, can you tell me about getting a MyDMV account?
If you are renewing by mail then you have to wait for it to arrive before you can create a MyDMV account