Maidsafe is a distributed store of key → value pairs. Every key->value pair (KVP) is signed that it is owned by X user. The KVP is encrypted by the end user in such a way that it can not be owned/viewed/modified by any other user. That KVP is linked to a particular user. Because of the self encryption used, if a user has access to a particular KVP not marked as public, it can be accepted that that particular user owns that data and that no one else can possibly have it (deduplication prevents it). D Irvine also said this data is immutable. It cannot be changed or copied or modified after it’s been created… So this data that can’t be modified or copied and is accessible to only one particular user - who then says “make sure this data can now only be accessed by person sending money to from now on” and sends that command to the network. The network changes the KVP to be owned by this new user. Transfer of value.
All of the hows of self encryption, file ownership, and how the network keeps track of who owns what is in the documentation.