Want to learn how to implement xbee wireless with arduino and eventually Pi

I am interested in learning/implementing the wireless Xbee technology and would appreciate any suggestions on what products to purchase to begin with, and then any books/tutorials I should obtain that would be good for a novice to get started learning/experimenting with them. This may be more information than desired on this forum but my overall goal is to use the xbees to connect various type sensors, as well as control signals, from remote xbees back to an arduino mega controller (and eventually a Pi for more processing power). I’d like to start with point-point and/or point to multi-point but eventually I would like to be able learn how to expand to a mesh type network after I get some experience under the belt. I currently have some limited experience with the arduino mega coding on a project that is currently monitoring 6 sensor inputs and controlling 5 outputs via a web page running on the mega. All connections to the mega are via wired connections which I would like to add the option of xbee wireless for more flexible and remote sensing and/or control. I would appreciate any suggestions. thanks

This is always a good place to start:

I visited the site but at 1st glance it looks like more advanced programming than I’m ready for. At this point, I’m not even sure what hardware (modules, adapters, etc.) that I would need to get started with programming and setting up a basic point-point ckt. I will browse thru it more thoroughly and if I get some basic info to get started tho. thanks for now tho.