A company's assets get paid for from three places. Picture a coffee shop: some of the machines and stock were bought with the owner's own money (equity), some with a bank loan (debt), and some things are simply not paid for yet, like flour delivered this week that the supplier will invoice next month. That last kind is money owed too, but it is short-lived, carries no interest, and is just part of everyday trading, so it does not count as debt here.
The debt-to-assets ratio measures only the borrowed money. A ratio of 0.30 means that for every $1 of assets the company owns, 30 cents was funded by interest-bearing debt, and the other 70 cents by the owners' money and those everyday unpaid bills.
As a rough guide, below 0.3 is low leverage, with room to borrow if needed, and 0.3 to 0.5 is moderate and typical of most businesses. Above 0.6 is high leverage, which is only safe for companies with very dependable income, because debt payments are fixed and due no matter how sales are going. A utility with millions of monthly bill payers can carry that load; a business whose sales swing year to year risks a bad stretch where the loan payments keep coming but the cash does not.
It gives a steadier read than debt-to-equity, which ignores those everyday operating bills and can shoot up artificially when equity is small, as with asset-light or buyback-heavy companies.