Low Resolution Pixels

How do you make an image into something that looks pixelated?
https://tofupixel.tumblr.com/738472174126612480/how-do-you-make-an-image-into-something-that-looks

so here is a tutorial for aseprite on how to crunch the colours of a photo like this into any palette!!

And here is a link to Aseprite: https://aseprite.org/

I should really take the time to learn how to use this software. I want to make pixel art so bad.