A Membase cluster communicates with clients in two ways; the primary way clients interact with membase is through manipulating data through various operations supported by membase. This is always through memcached protocol, and almost always through a client written for the particular programming language and platform you use.
In addition, there is also a RESTful interface which allows so-called "control plane" management of a cluster. Through this, a client may get information about or make changes to the cluster. For example, with the REST interface, a client can do things such as gather statistics from the cluster, define and make changes to buckets and even add/remove new nodes to the cluster.