Someone, typically a parent of guardian, reads them to you while showing you the words. After reading the story, they might go back and walk you through each word, how it's said, and its meaning.
Not only do a lot of kids learn like this, but for instance the little Polish that I know how to speak and read I learned like this as an adult with the help of a native speaker.
Oh wow. My parents never did this. I thought its something they only do in the movies…
That kinda breaks my heart. I loved my kids curled up in my lap while I read them their favorite stories. I wish every parent and child had that shared experience, and I'm truly sorry you didn't.
If it comes to pass that you have little ones of your own, please don't let that be something your kids only see in the movies. Make that your own new family tradition.