Hey kiddo, do you know what a bill is? It's a piece of paper that shows how much money you owe someone for something you bought or used.
Well, in Islam, a "billah" is a word that means "by Allah" or "for the sake of Allah". When someone says "Bismillah", which means "in the name of Allah", it's like they are asking Allah to bless what they are about to do.
For example, if you are about to eat, you can say "Bismillah" before you take a bite of your food, to remind yourself that you are sharing the meal with Allah and to thank him for the food.
People also say "Wallahi" or "I swear by Allah" when they want to express how serious they are about something they are saying or promising. It's like they are promising with Allah as their witness.
So when someone says "billah" or uses any phrase that includes Allah's name, it's important to take it seriously and remember that they are acknowledging Allah's presence and asking for his blessings.