Own and owe
What you own are your assets. What you owe are your debts. What is left over is yours.
In plain words
Assets are things worth money: cash, investments, a flat, a car. Debts (also called liabilities) are money you must pay back: a mortgage, a car loan, a card.
An example
You live in a €300,000 flat with a €200,000 mortgage. You own €300,000, you owe €200,000, and €100,000 is really yours.
Equity
The part that is really yours is called equity. For a person it is also called net worth. For a company it is what belongs to its owners.
What people get wrong
Buying something with a loan does not make you richer: what you own and what you owe both grow by the same amount. You get richer when what you own rises in value, or when you pay a debt down.