This was the first sling I ever made: https://www.slinging.org/42.html.  It's a simple string or Appu Sling. It's fast and easy to make and it's effective.   I mostly made my slings from boot laces in the beginning.  The beauty of it is that if you know how to do this you have the ability to make a sling quickly out of almost anything you come across.  If you want to improve it you can fill in the pouch by weaving or with  tape.  I find that medical tape works best but duct tape will also do the job.
    What was the first sling you made?

Jute balearics are the real gateway drug, made one for my first sling

I made my first sling out of nettles. I was interested in making fiber from plants myself and trying to weave it. I didn't have enough nettles for a whole sling, so I added a rope made of jute. .......the tail collapsed pretty quickly when throwing, and I repaired it and added synthetic threads to the tail.

The first slinging style I used was Apache.  For the first two months that's all I did.  Don't ask me why.

My first sling was a survival paracord shepherd sling, but recently I've been getting into making my own paracord baleric slings with the split pouch, which has been a ton of fun!