A GFCI outlet compares the current going out with the current coming back. If more than a tiny amount is going somewhere else, such as through a person, it opens in a fraction of a second. That is a different job from what a breaker does.
Where you need them
Kitchens, bathrooms, laundry areas, garages, unfinished basements and crawl spaces, outdoors, and anywhere within reach of a sink, tub, pool or spa. In Hawaii add covered lanai areas and outdoor kitchens, which see plenty of moisture even under a roof.
One GFCI device can protect everything downstream of it on the same circuit, which is why a dead bathroom outlet is so often fixed by resetting a GFCI in the garage.
Why yours keeps tripping
Nuisance tripping is usually not a nuisance. The most common cause we find is moisture in an outdoor box somewhere else on the same circuit, often one nobody has looked at in years.
Other causes: a failing appliance with a small leakage current, a long circuit with enough cumulative leakage to cross the threshold, a shared neutral between circuits, or simply a device that has aged out. GFCIs have a service life and thirty year old ones should be replaced on principle.
Testing yours properly
Press test, confirm power dies at that outlet and everything downstream, press reset, confirm it returns. Do it monthly. A GFCI that does not trip on test is not protecting anything, even though it still delivers power.
Newer self-testing devices check themselves and refuse to reset if the protection has failed, which is a meaningful improvement over the older style.
GFCI, AFCI and the difference
GFCI protects people from shock. AFCI detects arcing faults in wiring and protects against fires. They solve different problems and modern practice uses both, often combined in one device or breaker.
If you have an AFCI breaker tripping repeatedly, that is worth investigating rather than replacing with a standard breaker. It is usually detecting something real, such as a loose backstab connection.