IOS XR primer

http://tinyurl.com/n9sd77f

And of course, the Master Command Listing for IOS XR was
very helpful too.

Once you have all this down, you can then dig into specific
topics such as RPL, e.t.c.

Here is a good one on RPL.

https://supportforums.cisco.com/document/88676/asr9000xr-understanding-and-using-rpl-route-policy-language

 

http://www.cisco.com/c/en/us/td/docs/ios_xr_sw/iosxr_r3-5/xr12000_conversion/reference/guide/cnv_r35/cn35main.pdf

gives a baseline with some good info as to differences

and then move on to
http://www.cisco.com/c/en/us/support/ios-nx-os-software/ios-xr-software/products-installation-and-configuration-guides-list.html

which gives the in depth topic by topic.

https://supportforums.cisco.com/community/5996/xr-os-and-platforms
Document tab as well as Blog tab will get you expert at IOS-XR in no time.

ciscolive.com  pop “IOS-XR” into the search