Probability answers one simple question: out of everything that could happen, how big a slice is the thing I care about? That slice, written as a fraction, is the probability.
Counting the Slices
Take the spinner in the toy with four equal colours. Only one of them is brass. There are four outcomes that could happen, and one of them is the one you want, so the chance of brass is 1 out of 4 — written 1/4, or 0.25. You didn't need a special rule; you counted the favourable slice and divided by the total number of slices. That's the whole idea.
Theory Says One Thing — the Spins Prove It
The clever bit is the experimental tally next to it. Spin once and it's all over the shop: maybe you hit brass, maybe you don't, so the experimental fraction lurches between 0 and 1. Hit "spin 50 times" a few times, though, and watch — the experimental number stops jumping and settles right onto the theoretical 0.25. The more you spin, the more the doing agrees with the counting.
Why That Matters
It means the fraction you work out on paper isn't a guess — it's a genuine prediction of what really happens, just blurred a bit until you've done enough trials. Counting outcomes and rolling the dice are two roads to the same number. Everything else in probability is built on this one move.