Okay kiddo, so you know how politicians work in groups, right? Well, in some countries they have something called a parliament where a lot of politicians work together to make decisions for their country.
Now, a parliamentary private secretary (PPS for short) is like a special helper for a Member of Parliament (that means a politician who works in the parliament). A PPS is chosen by the Prime Minister or other party leaders to help the MP with their work.
The PPS's job is to help the MP stay organized, remind them of important meetings, help them prepare speeches and questions, and make sure they do their job well. Sort of like how a grown-up might have a personal assistant at their job.
But even though the PPS is there to help the MP, they still have to follow rules. They can't make decisions for the MP or speak for them in important meetings, because that is the MP's job. They just help them out behind the scenes.
So, that's what a parliamentary private secretary is. It's like a special helper for a politician who works in a big group of politicians.