So you know how everything and everyone is made up of tiny little things called particles? Well, there are two types of particles that we care about when it comes to charge: positive particles (like protons) and negative particles (like electrons).
Charge conjugation is when we take a particle and make it into its opposite charge version. For example, if we have a proton (which has a positive charge), we can use charge conjugation to turn it into an antiproton (which has a negative charge).
It's sort of like flipping a coin - if heads is positive and tails is negative, charge conjugation is like turning the coin over from heads to tails.
This might not seem like a big deal, but it's actually really important in understanding some of the fundamental interactions that happen in the universe. Scientists use charge conjugation all the time to study particles and figure out how they interact with each other.