Okay kiddo, so a proselyte is someone who decides to change their religion or beliefs and starts following a new one. This means they might have grown up following one religion or none at all, but then they learn about a different religion and decide they like it better.
So let's say a little girl named Sarah has never been to church before, but her friend takes her to Sunday school at her church one day. Sarah loves the stories she hears about Jesus and decides she wants to be a Christian too. She is now a proselyte because she used to not have a religion and now she is following Christianity.
Being a proselyte can be a big decision and sometimes it can be hard for people to accept. But it's important to respect and support someone who has made this choice for themselves.