Net worth is simply what you own minus what you owe. For a company, it is total assets minus total liabilities. For an individual, it is the same concept — add up everything you own (house, savings, investments) and subtract everything you owe (mortgage, loans, credit card debt).
For example, if you have assets worth $500,000 and debts of $200,000 your net worth is $300,000.
Net worth is the single best snapshot of financial health. A positive net worth means you have more than you owe. A negative net worth means you are underwater — your debts exceed your assets.