Think about when you go to Kroger or Walmart.

Every time, when you're checking out, that the person in there swipes an item over the barcode reader.

It goes, boop, boop, boop, boop.

Every boop is an event or a transaction.

And let's say that you went to the grocery store at Walmart.

Every time that thing goes, boop, the data is generated on what you bought, how much it cost, added to your bill.