You pay a premium and it disappears into an insurance company. Where does it actually go? Following the money explains more about how these policies behave than any brochure ever will, so let's follow it.
A slice covers the cost of insurance, the pure price of that year's death benefit protection. A slice covers the company's expenses. The rest, and in a well-designed high cash value policy it's the bulk, flows into the insurer's general account.
The general account is a giant, deliberately boring portfolio. Mostly long-term bonds, corporate bonds, mortgages, treasuries, bought to be held for decades and matched against the promises the company has made. Regulators require conservative investing here, and companies build margin on top of the requirement. This is why a whole life policy's guaranteed growth is modest, and also why the company can keep honoring the guarantee through recessions that flatten flashier portfolios.
Dividends are what happens when reality beats those cautious assumptions. Fewer claims than priced for, lower expenses, better bond yields, and the surplus gets shared with participating policyholders. That's why dividends move slowly in both directions, and why they can't be guaranteed: they're the difference between careful assumptions and actual results, and that difference can shrink. I covered the current climate in Why Dividend Rates Are Climbing After a Decade of Drift.
An IUL routes one slice differently. Instead of crediting you the bond yield directly, the company spends roughly that yield buying index options, which is what creates the market-linked upside and the floor. Same conservative engine underneath, different crediting method on top.
Why teach this? Because once you see the machinery, the sales claims sort themselves out. Promises of stock-market returns from a bond-backed product should raise an eyebrow. So should panic that the whole thing is a trick. It's a regulated, bond-backed savings engine with insurance attached, and it acts like one. How that engine compounds over the years is the subject of the how it grows page.