Ugh, this question is not being answered, and that link is mumbo jumbo to normal people.
Camosoul is jabbing at us, not you, just so you know,
@purplegreenred 
He is being sarcastic
I'm gonna give this a try, but it will need correction, because like most, I don't know exactly how any of this works
The wallet is a type of node, it connects to other wallets/nodes. Sentinel is another kind of node, and it kind of runs through or connects through the wallet node. It processes information and stores it in a database. It's a more sophisticated program than the budgeting system we had before. It can handle many variables and rules on how payments are made. But this is just the beginning. It will also process other information eventually, aside from the budgeting system. It may end up handling other databases, or the core team may choose to go back to mysql for a more complex database. By modularizing Dash, the main wallet can keep in synchronicity with Bitcoin, yet have completely new functionalities. Sentinel takes these functionalities that could create complications that mess everything up if directly applied to the core wallet, and runs them separately.
OK, so what is possible with Sentinel as it is now?
Imagine a contract that pays out in Dash, but in terms of US dollars. A quorum of MNs can quorie several exchanges, find out the going price just before payment superblock, and thus we don't over pay due to long term contracts, and at the same time, we can safely make long term contracts.
I believe Sentinel will also handle the future Evolution services such as name/password => account connections and the distributed sharded storage system.
So, it is the foundation, it handles all kinds of commands and can keep track of information. We just haven't created these sub programs to do other work yet.
I hope I got it right, and I hope smarter people will correct me where I've gone wrong. But mostly, I hope I helped you get the gist of what all this is about and why it's being done this way
