What is ErlSDB?

ErlSDB is an Erlang library to access Amazon's SimpleDB web service. It uses REST APIs to access SimpleDB service and is built on top OTP.
What is SimpleDB?

SimpleDB is Amazon's web service that provides persistence service for storing or querying a collection of key/value pairs. A collection of key/value pair is called an item, which is similar to row in relational database. However, unlike relation database you can store varying number of key/values. These items are in turn stored in domains which provide a naming scope.

I need to learn Erlang.