User blog comment:Planetn9ne/What do you need to create an OCF?/@comment-35470197-20181121232005

If you do not know the definition of ordinals in set theory, you need to learn it.

Next, you need to know transfinite induction, which an extension of the usual induction along natural numbers to ordinals.

After then, you can learn OCF, but you might feel that it is difficult. If you have knowledge of ordinal notation systems without using OCF, e.g. ordinal notations below \(\omega^\omega\), \(\varepsilon_0\), and \(\Gamma_0\), then it will help you to understand the strategy to create a larger ordinal from a smaller one using the limit of expressions.