The CC and BCC Header
If you are in the 'To' Header, it just means that the sender sends you the message, it is only you who the message is meant for.
If you're in the CC (Carbon Copy) header, it just means that you're being copied on a message aimed at somebody else. If you get a CC, that means the sender wants to inform you the message, but it is not actually aimed at you. You may be the boss or supervisor or someone who should be informed of the message.
The BCC Header
If you're in the BCC (Blind Carbon Copy) header, it just means that you're being copied secretly or hidden on a message aimed at somebody else. If you get a BCC, that means the sender wants to inform you the message and you may be the boss or supervisor or someone who should be informed of the message secretly.
Please look at what Honorable Chairman Sir has already talked about.