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.