Electromagnetism

What are the basics that you must know for electromagnetism? Cause I have a test on it tomorrow afternoon and know absolutely nothing. Literally the hardest topic in Physics for me to understand for some reason.

Mate this is such an open question you can't expect someone to sit here and summarise an entire field of physics?

Take some initiative, whap out your textbook and look at how the chapter is broken down in the contents to get an idea of what's in it, then revise what you can in the time before the test.