To develop and configure a new custom ALE scenario, comprises 5 steps:
1. Design and develop the custom IDoc with it’ s segments and a new message type
2. Configure the ALE environment with the new IDoc and message type (customer model,
partner profiles and linking IDoc to message type)
3. Develop the outbound process which does the following:

1. Populates the custom IDoc with control info and functional data
2. Sends the IDoc to the ALE layer for distribution
3. Updates status and handles errors

4. Configure the ALE inbound side (partner profiles with inbound process code)
5. Develop the inbound process which does the following:

1. Reads the IDoc into a BDC table; selects other data that is required
2. Runs transaction using call transaction or BDC session
3. Updates status and handles errors

View/Download the Complete Guide on ALE Configuration and Development.

Beginners guide on IDOC and ALE to teach you about:

IDOC

What Is IDOC.
What are the main advantages of IDOC?
Difference Between EDI and IDOC.
Delete/Remove of IDocs from R3.
IDOC Components & Structures.

ALE

ALE - Introduction
Data Distribution Model
ALE Process
ALE Functionality
ALE Converters

This Idoc Creation Procedure (Step by step Guide) will teach you with all the instructions on creation of Inbound and Outbound IDOC with screen shots for better understanding.

Download the Article from Rapidshare or Mediafire.

Nice article from a guy in Infosys showing the clear steps on archeiving IDOC. Here is the link to sdn. Download the Archieving IDOC(PDF File) from sapdb.