> Like who is the police in all this?

It's not that there's an agency that tracks the amount of money and the "value" of goods and services and runs around changing prices to match. It's that, if you have more money, you're more likely to spend it, which means you'll accept a higher price on items. Since you're willing to pay more, companies will raise prices to match. That's what causes inflation.

Repeat this millions of times because all that extra money you spent means everyone else has more money, so they are willing to spend more, which means companies can raise prices, and the cycle continues until you're at new "stable" prices that are simply higher than the original prices, roughly proportionally to the extra money that was injected.