Okay kiddo, so when the Catholic Church talks about "validity" and "liceity," they're talking about whether something that happened in the Church is actually allowed and acceptable.
Let's start with validity. This means that something that is done in the Church is done in the right way according to the rules that have been set up. For example, when a priest gives someone Communion during Mass, it is only considered valid if the priest uses the right words and gestures that have been established by the Church. If he doesn't do it right, then the Communion might not count, because it wasn't done the right way.
Now, liceity is a word that means something is legal or allowed by the rules of the Church. So, for example, if a priest wants to do something that is not allowed by the Church's rules, like getting married, then it would not be considered licit. If something is not licit, it is not allowed and should not be done, even if it seems like a good idea.
So basically, validity and liceity are two ways that the Catholic Church makes sure that everything that happens within it is done in the right way and follows the rules that have been established.