Okay kiddo, let me explain it to you like you're five.
A state university system is like a big group of schools that are run by the government of a state. Imagine you have a bunch of toys, all different kinds of toys. Now imagine that the state government is like your parent or guardian, and they are in charge of all the toys. They want all the kids in the state to have good opportunities to learn and get an education, so they decide to organize all the different kinds of schools into one big group, called a state university system.
This big group of schools can include all sorts of schools, like big schools with lots of students or smaller schools with fewer students. They can also have different focuses, like schools that specialize in sciences or schools that focus on the arts. Each school in the group still has its own name and its own unique things it can offer students, but they all have to follow the rules set by the state government.
When someone wants to go to college, they can look at all the different schools in the state university system and pick the one that best fits what they want to study and how they want to learn. And because all the schools in the state university system are run by the same government, they have to follow certain rules about things like tuition costs, admission requirements, and how they teach.
So, in summary, a state university system is a big group of schools run by the government of a state that offers lots of opportunities to learn and get an education.