Coleg Cymraeg Cenedlaethol is an organization in Wales that helps people learn and study in the Welsh language. Just like how you learn and speak English in school, some people in Wales want to learn and study in Welsh so they can keep their language and culture alive.
The Coleg helps people do this by working with universities and colleges to make sure there are courses and programs available in Welsh. They also offer scholarships and support to students who want to study subjects like science, business, and literature in Welsh.
So, Coleg Cymraeg Cenedlaethol is kind of like a helper for people who want to keep the Welsh language and culture strong. They make sure people can learn and study in Welsh and help those who want to do so succeed.