Hey there, I know it is not easy to understand about this function at first. But the aggregate itself means to collect or gather into a mass or whole. For example, the census data were aggregated by gender. Other meaning, to amount to (a whole sum or total): total audiences aggregating several million people.
It helps us to 'extract' the meaningful insights from the data. In R, we use aggregate by whatever parameter inside the bracket could be mean, median, etc. That's how it works 