According to Apple\'s ARC Documentation, there are a fairly significant number of changes to the way that one develops software when using ARC.
As a complete beginne
Apple itself recommends ARC for new projects. http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/MemoryMgmt/Articles/MemoryMgmt.html#//apple_ref/doc/uid/10000011i
read point 2 in At a Glance
There is sooo much more interesting to learn in Objective C & iOS apart from the memory management. My advice : Don't bother about MRR