A creationist cosmology is a belief about how the universe was created, based on religious teachings. According to creationists, the universe was not formed by natural processes like the Big Bang, but rather it was created by a divine being, such as God.
Imagine that you're playing with your toys, and you create a brand new toy using your imagination and your own hands. This is kind of what creationists believe happened with the universe - except instead of you being the toy maker, they believe God created the universe by simply speaking all of its parts into existence.
Creationists believe in something called "intelligent design," which means that everything in the universe was put exactly where it is by God for a specific purpose. Imagine you're playing with a puzzle, and every time you put a piece in the puzzle it fits perfectly and creates a beautiful picture. Creationists believe that the universe is like that puzzle - everything fits together perfectly and was placed exactly where it needs to be by God to create the world we live in.
Now, some people might believe this is not how the universe came to be. They might believe that something called the Big Bang theory is responsible for the universe's creation. But creationists don't believe in that theory - they believe in God's story of creation instead.
So, in summary, creationist cosmologies are the beliefs that the universe was created by God and everything in it has a purpose. It's like a toy made by an incredibly skilled toy maker. While there are other explanations for how the universe was created, creationists believe that only God could have created something so perfect and intricate.