Where should I start to get better at modding

I have no idea what I'm doing

 

start with something easy like skins, license plates, then gradually go to something more difficult

 

This is a good place to start but if you want to do modelling stuff start but just making a simple part for an existing car for example a roof scoop or roof spoiler as those don't need too much or any jbeam you can just group them to the body node group usually.

 

Yes
The easiest part to make would be something in interior, because it only needs 3d model, textures and dont need jbeam

 

How do I add a part to the interior

 

open up the vehicle .dae in blender
you should be able to find it in the vehicles folder

 

hood scoops and spoilers don't even really need textures to look good, so that's even easier. interior elements still need jbeam editing.

 

I meant like mod slots, coding, etc

 

now that, i’m not entirely sure of, but I know that the preferred program is notepad++

 

this is a good tutorial if you want to make simple things like bodykits. covers pretty much everything except how to edit the jbeam physics structure.