I grew up watching Full House. I love it. I ended up watching all the episodes a few years ago, all seven seasons. I would say you don't have to watch Full House to understand Fuller House. But it does help in the same way you don't have to watch Boy Meets World to understand Girl Meets World. But it does help to understand Cory better. It adds depth and meaning. So, kids can connect to the newer characters which can be good. Some of them will end up going back to watch the original series too which I think is amazing. So, same thing with Fuller House.
Fuller House is a fun show. The style is a little different than Girl Meets World. Fuller House is more focused more on comedy. Girls Meets World is more revolved around the classroom at school. Fuller House is more focused on the house and generally has a lot more characters. Girl Meets World has more kids and more of a focus on the kids than Fuller House.
Fuller House is focused on several families that are friends with each other. It's mostly focused on one family plus their neighbors, friends, etc. But the family is a bit bigger than the main family on Girl Meets World. There are roughly five main kids and teens that Fuller House focuses on and there were sometimes a few other kids too.
The two main adults in Girl Meets World is Corey and his wife. Fuller House has four main adults who were kids in Full House. So, we get to see these four adults and their kids in Fuller House. Girl Meets World focused on Corey's family. But in Fuller House, the story revolves around two main families. And those two families came from two girls who were best friends in Full House. They grow up and end up having kids and being neighbors.
Fuller House focuses on three single women. One woman is DJ who has three sons. But she is a widow. The 2nd woman is her sister, Stephanie. But she has no kids. The third woman is DJ's best friend, Kimmy. And she has one daughter named Ramona who is sort of like Riley from Girl Meets World.