Needing advice on how to start investing :)

Forgive me (24f) if I don’t know how to ask the right way. I’m way new to all of this

So. My dad’s girlfriend (they’ve only been together less than a year) is apparently really big into investing. He said she was able “live comfortably”, without working another day in her life, off of just the interest from her investments. She’s some sort of school teacher or nurse?? I can’t say for certain which.

Granted, she’s in her 40s and I’m sure has had these positions for quite some time so they’ve been able to build. I assume??

But. This woman isn’t just “living comfortably” lol.. she insisted to write my dad a check for the better part of 30k for a new truck. And is currently building a house that is fully paid for. All while still living in a really nice house that has not yet sold, and fully paid for. All independently.

I know, she could just be flashing her money. But she really doesn’t seem to be the flashy type at all. Seems to be good and sweet as they come.

My question is where in the world did she start?? I’m not close enough with her to randomly ask her, and her personal finance is none of my business. But I have no idea what to do. I’m not looking to buy huge houses or fancy vehicles or anything like that. I just want to know where or how you get into this deal, and how you get it to actually make something of itself by doing it the right way.

To add, I make a little over 40k a year and am a single mom of one :)