Certainly before you learn it you have to know about App Engine. What is it? Google will teach you, just visit this link:
Ok! now what is slim3..
Slim3 is a low level API that easier to be learned than JDO or JPA. It is a kind plugin for eclipse. The concept of slim3 is MVC (model, view, controller). With slim3 we can access the data from the datastore more quickly than JDO/JPA. Why? Because slim3 does not use PersistenceManagerFactory/EntityManagerFactory which is known as a slow starter and avoids extra initializations carefully.
There are three parts of slim3 that i will try to explain:
