For undergrad level cosmology you need to know calculus and some basic knowledge about differential equations.
After learning the math part you can focus on the physics part of the cosmology..
cosmology, field of study that brings together the natural sciences, particularly astronomy and physics, in a joint effort to understand the physical universe as a unified whole.
The “observable universe” is the region of space that humans can actually or theoretically observe with the aid of technology..
Cosmology is a branch of astronomy that involves the origin and evolution of the universe, from the Big Bang to today and on into the future.
According to NASA, the definition of cosmology is "the scientific study of the large scale properties of the universe as a whole.".
Your qualification should be in a physics-, mathematics- or astronomy-based subject, or a subject with significant mathematical or physical content, and include modules in calculus, differential equations, mechanics, electrodynamics and quantum mechanics..
