how to start with tc

I’ve got into C++ a while ago sole purpose of working with the core, but dropped it some time later, and now I thought I’d give myself another try, but I have no clue where I should start from.
The title speaks for itself, I’m asking you what should I go through first and why, and if there’s actually anything that I can use for guidance, besides the dim, incomplete documentation.

You may consider me incompetent (and to a certain extent, I am) but I genuinely have no idea what to begin with.

http://collab.kpsn.org/display/tc/Installation+Guide ?

Welcome in TrinityCore.

You can start trying to implement some http://www.trinitycore.org/f/topic/8146-random-trinitycore-ideas/

Last time I did one of those in order to practice with C++, I’ve implemented a simple Quest Tracker https://github.com/TrinityCore/TrinityCore/pull/13353

We lack of documentation, this is true, but you can always ask in IRC channel for help and check commits to view examples.

Pulling with average speed of 15KB/s is frustrating.