Any chance you had a look at this document:
There are numerous links available in SDN which can be accessed via a simple search.
I suggest you do the same before you post a query next time.
Till then here are some references;
Configuration steps required for posting idoc's(XI) -
ALE configuration for pushing idocs from SAP to XI -
Check the following links for sending Idocs from :
2) PI to R/3 :