Féabar wrote:
A Bhreandáin:
When do you use the "na"? I've never really figured that out.
Féabar
As Lughaidh has already said,
na is used with the genitive singular of feminine nouns and the genitive plural of nouns of either gender.
The only time you would normally use
na with a place name is if the name of the place starts with an article and is feminine singular or is plural.
Countries are usually feminine and often start with an article, e.g.,
an Fhrainc,
an Spáinn, etc., so you often see
na in the genitive of a country name, i.e.,
na Fraince,
na Spáinne, etc.
One exception to that general rule is
Éire, which doesn't have an article in the nominative but becomes
na hÉireann in the genitive, i.e.,
ceol na hÉireann,
mná na hÉireann, etc.
Here's a list of other country names:
http://en.wikipedia.org/wiki/List_of_Irish_exonyms