During Hack the Rainbow, two of the NEAR Collective's team members - Matt Lockyer and Sherif Abushadi - gave a webinar on NEAR accounts and Key Registration. They took the time to explain how NEAR accounts, contracts, and keys work.
Shortly after, another awesome developer and member of the NEAR team, Mike Purvis also did up an excellent overview of NEAR accounts/keys. Highly recommend you take a few minutes and watch it as well.
Having watched both of these a couple times, I finally decided that the only way to fully understand what's going on is to try and teach it myself by putting into practice what they're talking about.
So, this is my deep dive into NEAR accounts, contracts, and keys. My end-state for writing this multi-part tutorial (and hopefully yours for reading it), is to completely understand how accounts, contracts and keys work together opening up cool possibilities for projects.