WireGuard uses something called a private key and a public key. The private key is private and should never be shared with anyone else, but the public key on the other hand is what your device use to authenticate with our servers and is similar to a username.
The private key and the public key is known as a key pair; meaning each private key has a public key equivalence, so without a private key, the public key is useless, which is why it is so important that the private key is kept, well, private.
While you can use the same public key on several devices and configuration files, only one connection with a specific public key can be connected at a time. This means that most of the time, if you intend to have multiple devices connected at the same time, you will want to use a different public key for each device.
Only four public keys can be generated at a time. You can manage your public keys on our website under Profile → Key Management