You can use this phrase to describe how well you understand something. It's an intelligent-sounding phrase. In the situation above, you could also say:
I don't know much about Korean politics.
But this version doesn't make you sound as intelligent as the original version.
Other adjectives that you can use with "have a ___ understanding of ___" include:
She'll probably have a better understanding of what's going on.
We now have a deeper understanding of the ecological effects of greenhouse gasses.
We want to make sure that all students have a basic understanding of Algebra.