Hi, when u use methods of Sharepoint Javascript API , what exactly happens? Under it is a webservice? or simple http protocol that comunicates with Sharepoint? And can it be used anonymously or only when logged in? Do I must provide some credentials to use it?

take a look at this it may provide you with some idea http://msdn.microsoft.com/en-us/library/ee538253.aspx

thanks! JSON is the answer and the protocol is just http. in URL it uses /_vti_bin/client.svc propably The client object models are provided through proxy .js and managed .dll files, respectively, which can be referenced in custom applications like other object models. The object models are implemented as a Windows Communication Foundation (WCF) service (.../_vti_bin/client.svc ), but uses Web bindings to implement efficient request batching. All operations are inherently asynchronous, and commands are serialized into XML and sent to the server in a single HTTP request. For every command, a corresponding server object model call is made, and the server returns a response to the client in compacted JavaScript Object Notation (or JSON) format, which the proxy parses and associates with appropriate objects.