I'm on mobile right now so I won't be able to provide any links. I'm not really a regular here at TrinityCore but I do contribute some things once in a blue moon.
In terms of resources find the TC wiki, that will give you some (used to be limited, I don't know how is it now) information about the core. To get started I'd recommend taking a look at the bug tracker for something that looks easy to fix then just trying to do it (I'd suggest avoiding anything including packet structures and reverse engineering at the very beginning).
Sadly there is no end all, be all guide for development. You have to figure stuff out on your own mostly, and if you are really impossibly stuck you can try asking for help on the TrinityCore IRC channel. Luckily the core's code is generally very clear and well written so most times you should have little trouble understanding how something works. Finally, remember, Google is your friend.
I whish you good luck on this adventure, friend.