"Well, there are an awful lot of wizard fires to choose from, you know,
but as long as you've spoken clearly -"
Using the Floo Network is much simpler than Apparition; it can be done by an underage witch or wizard who hasn't even started school yet (CS4), whereas Apparition requires a few months of tutoring and supervised practice for most witches and wizards to be able to perform it (HBP17). However, while using the Floo Network is easier than Apparition, it is also less flexible in terms of where a user can go; it can only take one to a destination that is connected to the Floo Network.
The Floo Network is made up of various wizarding fireplaces all over Britain. When Floo Powder is thrown into a fireplace that is connected to the network, the fire will burn a brilliant green and assume a state that allows a witch or wizard to enter the fire without being burned, at which point he or she will state the name of another Network location and then be connected to that location in a spinning rush of emerald green flames. While in transit, the user will be aware of other grates rushing past, but too quickly to be perceived clearly. If desired, a witch or wizard using the Floo Network may use it only to speak with another Floo connection rather than to travel there (GF11, GF19).
It is important to state the name of the intended destination very
clearly so as to avoid being connected to the wrong location, and
it is also important to keep one's elbows tucked in. The Network's
function, in fact, is something similar in principle to the use of
a Muggle telephone; giving an incorrect destination is like dialing
a wrong number.
After Voldemort and his minions assassinated Minister of Magic Scrimgeour during the Second Wizarding War and took over the Ministry of Magic, only senior Ministry members were permitted to connect their homes to the Floo Network (DH12).
See also Floo Regulation Panel / Floo Network Authority.
Known Floo Network Connections