atá means "that is" in the sense of "Here is the book
that is required for the course."
Generally speaking, when
a* is directly followed by a verb, it means "that" or "which". In other words, it introduces a relative clause. In almost all cases, there's a space between
a and the verb, but not before
tá. Instead of
a tá, we write
atá.
You might find this article helpful:
viewtopic.php?f=34&t=841* Note that I'm talking about
a without a fada.
á followed by a verb has a different meaning.
_________________
賢いふくろぐま
Seans Eile - free software to help you practice your Irish
Scéala na Wombait - Muddle-headed Memes and Musings