They are both Ground Fault Circuit Interrupters and can be either a wall mounted receptacle type or a panel installed breaker type.
Either is required to be installed, by code, to protect persons against electric shock, around ponds swimming pools, bathrooms, laundry rooms, garages and other situations where water/moisture could cause problems.

Around a pond the receptacle type monitors the pump, a UV Light or any other device, that is plugged into it and Should trip the power in a ground fault condition. It would cost you about $20.00.

A panel installed GFCI breaker protects the whole circuit, against overload and ground fault all the way out to one or more ordinary receptacles and whatever is plugged into them. It could cost you about $100.00.

Ether type should be checked/tested every month [see manufacturers instructions] to be sure it is working properly. They have been known to fail during a ground fault situation.
"Horton"

heres one i found on the lowes website and its $35 is it the right type? http://www.lowes.com/lowes/lkn?action=productDetail&productId=12812-296-HOM120GFI&detail=desc&lpage=none

and what's the white wire hanging there for?

The white wire coming out of the Square D, 20Amp single pole, GFC breaker, shown there, ties onto the neutral bar in the breaker panel.
Without it being tied in, the breaker would not function under ground fault conditions.

If I were you, since you did not know what the white wire was for, I would seek professional help, in doing the installation.
It maybe safer for you!
"Horton"

Dont double a GFCI (breaker box mounted) and a GFI (socket type).They will work against each other and odd things will happen. One or both would will trip with any flucuation of current.

If you are adding a seperate circuit and the house is open to run new wires then a GFCI breaker in the box would be better. (recommended)

If adding to an existing circuit then the GFI recepticle would be best.

As I recall years ago, Article 100 NEC states a GFI is a motor protector, a GFCI is a people protector. Further I checked the prices on line, a HOM120 GFI lists for $141.00 a HOM120 GFCI lists for under $40.00. Go figure.

GFIC and GFI are the same thing.
Both sets of initials are used for the same device, be it a breaker type or a wall mounted/ receptacle type.

Ground Fault [Cricuit] Interrupters have nothing to do with electrical motor protection.
They are required by code, to be installed, under certain conditions, to protecting people against electrical shock.

Below is an extract from an article by Larry Dimock, in which he explains the use of the initials, GFCI and GFI.

GFI or GFCI
A ground-fault interrupter. A device to prevent electrocution, which serves also as a receptacle or (less commonly) as a breaker. I consider the letters "GFCI" confusing because they stand for "ground-fault circuit interrupter" and the word "circuit" is vague and distracting. "GFI" clearly states the function it performs: "ground-fault interrupter". Since 1973 Code has required GFI protection for more and more receptacle locations in homes. If connected to properly, a GFI receptacle is also able to sense and disrupt ground-faults at any standard receptacles wired on from it. Learn More about GFIs.

The link below is to the complete Larry Dimock article

Here is a link that might be useful: Article by, Larry Dimock.

Would it not be better to have a ground fault receptacle near the pond as compared to a GFI breaker at the box inside you home? Especially if the outlet at the pond is a distance from the breaker box in the home. I think milliseconds would count when being exposed to electrical voltage and the distance to the interrupter would matter.

We have three 20 amp receptacle boxes at our pond and a dedicated GFCI breaker box is located 20 feet away at the side of the house.
The electrician did it that way to protect the line to the receptacles as well as the receptacles.
Even though the line is buried in conduit, if for some reason it is ever torn up by digging equipment etc., It will trip the breaker.

John, it is so quick that it should trip before you could blink your eye or your heart makes a beat.
I can remember seeing a demonstration of a prototype GFCI back in the 1960's and man did that device trip the circuit fast, it seemed instantaneous, no matter the distance from the actual ground fault's point of contact.

The way lsst's electrician did the installation is the Cadillac way, of covering all the bases, everything from start to finish, is protected against a ground fault.

But having a GFCI receptacle adjacent to the pond is all the NEC/CEC require, to protect a person from electrical shock injury/death. The latter, is of course, the less expensive way to do the installation. But it is equally effective in saving a life, if all conditions are met*.

At a trip speed of less than 1/40th of a second from a current leakage of 5 milliamps the GFCI's internal trip circuit is reacting super fast, but you could, depending on the person and other circumstances,still feel a real "kick" from that 5millamps of current entering your body.

Example. If you were up a ladder, you could easily fall off it, due to your reaction of that quick short shock and die from the fall.
* If you are interested, you could read the two bottom paragraphs in this other article about GFCI safety, that I have linked below.
"Horton"

Here is a link that might be useful: GFCI Safety.

I have a GFI out by the pond. Why? Horton would say it's because I'm a cheap Yankee!! LOL And while that may be true, the real reason is that I'm too lazy to walk all the way back to the circuit breaker box every time I have to reset it. And, yes, I do manage to trip it periodically when I plug/unplug something.
---David

Don't know what the codes are in US but here the GFCI breaker is requirred on all outdoor wiring and must be a separate line from any other receptacles. IOW all outdoor plugs must be on a separate circuit with a GFCI breaker in the house box or garage wherever electrical panel is.

The Prof said,
"And, yes, I do manage to trip it periodically when I plug/unplug something."

That should have read " Cheap & Klutzy Yankee"! LOL
Keep the didgits clear Prof!

Jalal, the U.S. electrical code, [NEC] requires the same type of installation for GFCI's, as that in Canadian code [CEC].
"Horton"