XI-Connecting to R3

Hi Experts,

I am new to XI. I have an R/3 System. I have an XI system.

At present i dont have any connection between them. I want to do File to IDOC scenario. What are the basic connections required between my R/3 and XI. How my XI system know about R/3.

What are all the possible settings i need to for File to IDOC scenario.

Let me know the things after ALE-IDOC creation.