Logger for Google App Engine is a simple REST based service used solely for logging purposes. All messages are posted to private namespaces using an authorisation key using an HTTP REST API.
Log messages include standard severity levels (Debug, Info, Warn, etc.) and a custom identifier (e.g. source).
Before you can post, you will need to register a namespace or two. Once you have done that, note down the authorisation key for each namespace. You will need to include this in your request for security reasons.
You may want to use a REST client to play around with the API such as RESTClient.
Refer to the Log4GAE Wiki for further documentation.