Like what? An infinite decimal that seems random that we can calculate down to more and more precision?

That's pretty easily answerable, if that's what you're asking. Pi is how we measure the circumfrence of a circle, amoung other things. But a circle has no edges. So how can we use numbers to calculate the infinitely smooth line of a circle with no corners if numbers inherently make precise, "edged" digits?

You use an infinite number. Precisely, Pi, which we calculated by taking the circumference of a circle and dividing it by the diameter. The more precise we can measure the circumference and diameter, the more digits of pi we can get. The more digits of Pi we get, the more accurately we can measure the circumference of a different circle we don't already know.

TDLR: Pi is like that because circles don't have edges, so we need a number that doesn't end, otherwise when we calculate a circle and, say, put it into a computer, it'll have little edges. The less numbers of Pi we have, the more noticeable and numerous the circles' edges. Its like the difference between having a screen with more or less pixels.