Okay kiddo, have you ever heard of a calendar? It's like a special chart that helps people keep track of time. Well, the Seleucid Era is a way of measuring time that was used a loooong time ago by a group of people called the Seleucid Empire.
Now, this empire was in charge of a lot of different places, like parts of Greece and Asia. They wanted to have their own way of measuring time, so they came up with the Seleucid Era. They started counting time from a specific day - the day that one of their kings became ruler.
So imagine this - you're playing your favorite game and your mom says "okay, we're going to start playing from the moment we finish our lunch." That's kind of like what the Seleucid Empire did with their calendar. They said "okay, we're going to start counting time from the moment that this king became ruler."
And just like you might say "it's been two hours since we started playing," the Seleucid Empire used their Seleucid Era to say things like "it's been 100 years since this king became ruler." This helped them keep track of important events and historical dates.
Nowadays, people don't really use the Seleucid Era anymore because we have different calendars and ways of measuring time. But it's still an important part of history and helps us understand how people used to keep track of time.