How do I start off first

I mean where do I start coding i know what a function is but I dont know were to start

Lazydevs basic shmup tutorial on youtube is a good start. He goes through all the basics. I only got about halfway through before I started to figure out stuff by myself.

Understand the basics. Get to grips with displaying a character on the screen and moving it about using the keys - this really should not take long.

Think about what you want to achieve, make a list and start thinking about how to achieve the items on the list.

I agree with @Doriencey - check out the Lazydevs tutorials. They are really food.

Good luck

definitely recomend you nerdy teachers.
Also their youtube tutorials because they are very easy to understand and relative short.
Wish you fun. :)

I don’t love videos, so I started with these resources:

https://sectordub.itch.io/pico-8-fanzine-1
https://mboffin.itch.io/gamedev-with-pico-8-issue1
https://mboffin.itch.io/pico-8-top-down-adventure-game-tutorial