I have no good knowledge on mechanics and I want to be able to do mods / repair a car, where do I begin?

I am a yr11 Aussie high school student 2 months off of getting my license.

I love 4x4s and I’m getting a 2003 Pajero when I get my license, I want to know how to modify and fix my car when I need to but I have no idea where to start.

People who are mechanically skilled, where did you start? And how long did it take to get to your skill now?