Certain assets are worth borrowing money for. We can call these investments. Borrowing to go to college, to purchase a house, or to buy an automobile are all investments; these are good debt. A house is an investment because it will appreciate in value and will save you rent, while education is an investment because it will lead to a better job and higher income. An automobile is an investment because you will likely need one to commute to your job.
Bad debt is borrowing for consumption. Do not borrow on a credit card unless you can pay it off at the end of the month. You do not really need that 55-inch TV; you can buy it if you have the money to buy it, but do not finance it with a credit card. Of course, if you are unemployed and need to use your credit card to buy food, that is another matter. In that case, the hopeful outcome will be that you will find a new job and the credit card debt will just be temporary.