Cash account

This type of account asks you to deposit cash, and then you can use that cash to buy stocks, bonds, mutual funds, etc. It's not much more complicated than that.

Margin account

The cash and securities in your account act as collateral for a line of credit that you take out from the brokerage in order to buy more stock. The interest rates that brokers charge, while below typical credit card rates, make the return that you need to earn on your investments much higher than if you're only investing with your own cash.

There is also an "Option account", which allows you to trade options.  The type of account is a much riskier since you are dealing with options.

If you are interested, you may find the article below might be helpful.

http://client.nextvenue.com/harrisdirect/MarginTutorial/staging/mt_section01_bottom.htm

simply speaking:

margin account you can borrow money from your broker.

cash account: not.

you can get wiped out using margin account, you can also get wiped out using cash account.

if you are a savy invester, margin account provides "other people's money"

if you are not a savy invester, even with cash account, you can lose your pants.