A GFCI outlet (which stands for ground fault circuit interrupter) is a receptacle with its own built-in circuit breaker. It is intended to protect you from electric shock and your wiring and breaker panel from being "shorted out".
Building codes require that you have a GFCI outlet in areas near water (e.g. in your kitchen, bathroom or garage.) You don't need to install a GFCI outlet for all your outlets near water, just the first one in a series. This way the single GFCI can "trip" or shut off if one of the receptacles further down the line are shorted out.
Electrical basics are easy to understand, but working on electrical projects can be hazardous. You should always take the proper precautions – turn off the circuit you are working on and use tools with insulated handles. For complete, step-by-step instructions for this DIY project, watch this friendly and straightforward video tutorial.