Message Type: For which purpose the IDOC is going to fire.
IDOC Type: It contains exact structure, in which sequence data transfered from
one system to another system.
Through Message Type a whole bunch of data transfered to process code/port for transferring data.
IDOC type/Basic Type contains exact data.
Please try these transaction codes.
WE82 - Message Type and IDoc Type
WE64 - Process Codes (Inbound and Outbound) for Message Type.
Message type. A message type represents the application message exchanged between R/3 systems and R/3 and an external system. A message type characterizes the data sent across systems and relates to the structure of the data called an IDOC type (see below). For example, MATMAS is a message type for Material Master, and INVOIC is a message type for an Invoice (Billing Document). ALE supports over 200 message types in R/3 and about 200 application areas.
IDOC type and IDOC. An Intermediate Document (IDOC) type represents the structure of the data associated with a message type (DEBMAS02 for message type DEBMAS Customer Master, and WMMBID02 for message type WMMBXY Goods Movements), while an IDOC is an object containing the data of a particular message type. IDOCs are data containers with intelligence built in. Each IDOC contains one and only one business object. For example, an IDOC of type SHPMNT01, message type SHPMNT, will contain data only of one Shipment Document. Generally, the architecture of an IDOC is independent of the message type by virtue of ALEs ability to redefine it for any message type.
Use transaction BD64 or the following menu path to maintain the model: From the IMG (Implementation Guide), Cross-Application Components -> Distribution (ALE) (*) -> Distribution Customer Model -> Maintain Distribution Customer Model Directly -> Maintain Distribution Customer Model Directly.
By using Tcode WE82 we can create the Message type and also it displays the exitsting Message type along with IDOC and table name is EDIMSG.
Coming to Procees code :
You can find link with all details like One funtion module corresponding Process code, Message type, and IDoc etcc... by using T-code -WE57, for this press'positon' button and u will get one screen in that press 'F4' then it will opens other screen wich it clearly shows all details.
or you can go directly by using table -
TMSG1 (Logical Messages and Process Codes in Outb. Procg)
TMSG2 (Logical Messages and Process Codes in Inb. Procg)