This container is used in OnPhotonSerializeView() to either provide incoming data of a PhotonView or for you to provide it.
The isWriting property will be true if this client is the "owner" of the PhotonView (and thus the GameObject). Add data to the stream and it's sent via the server to the other players in a room. On the receiving side, isWriting is false and the data should be read. Send as few data as possible to keep connection quality up. An empty PhotonStream will not be sent. Use either Serialize() for reading and writing or SendNext() and ReceiveNext(). The latter two are just explicit read and write methods but do about the same work as Serialize(). It's a matter of preference which methods you use.