1: Debt + Equity = Enterprise Value. The value of the equity is determined by the stock markets - and that value can vary a lot.
2: Equity Value therefore represents the market's perspective of the Net Present Value of the future cash flows less the value of the debt. Those flows, calculated using a discounted cash flow spreadsheet, could be from profits, or could be from sale of assets.
3: The analysts will forecast the Enterprise delivering a certain IRR - annualised percentage return, which is split between the debt and equity. This total return is called the weighted average cost of capital - WACC.
4: Debt is cheaper than equity, and it also has a lovely tax shield effect from the interest expense.* Debt holders get the company when the value falls underneath the total value of the debt though, so you don't want to issue too much.
5: Equity (shareholders) demand much higher returns than banks, but accept the greater risk for it. e.g. VCs have much higher expectations than banks about their returns.
6: The more debt you have the higher the returns - and risk - for the equity. Think about the leverage you can get on a house - an asset with low % returns can deliver high value (or high loss) by using a lot of bank debt.
7: There is a body of work around finding the optimum level of equity and debt for a company - basically you want to balance the risk from having too high debt (and the company value falling underneath that value and using all the equity) and the benefits of higher returns to equity=holders from having higher debt.
Going back the the original post - EV is the real value of the company, not market cap. Ford could sell down their debt by issuing more equity, Tesla could issue debt and reduce the share of equity. It all comes back to EV.
*This makes the weighted average cost of capital vary slightly as the amount of debt changes.