A lot of people around the world have their secret(private) and public keys. They make their public keys opened for everyone and keep corresponding private keys in a secure place. Public key can be used by anyone to encrypt data, but only an owner of corresponding private key can decrypt the data.
For example, you decide to send an encrypted container to your friend John. John may have his public key created earlier and stored on a Public Key Server in Internet. John may also send you his public key attached to e-mail. As soon as you get John's public key, you can encrypt the container with this key and send it to John. After receiving the container John will be able to access data with his secret key.
BCArchive includes the BC Key Manager utility to manage your own public/secret key pair as well as public keys you have received from other people. You can run Key Manager utility from BCArchive Program Folder or using Manage Key Database command in menu of BCArchive main window.