I am teaching myself Gaeilge from Micheal O' Siadhal's book "Learning Irish", and I have reached the point where he discusses "a" in regards to placing it before "Ta", in order to make "ata". I understand how the process works but his explaination of what it means has left me confused. Could some person wise in the ways of Irish grammer explain how and when it's used and what all of it's meanings are?
Go riabh maith agat!
PS: I forgotten what that little "a" placed in front of "Ta" is called. The failure to grasp the lesson left me so distressed that I have not picked up the book in months! Help!

One conText is in a question:
You'd say; Tá sé....(He is....)
But Céard atá sé....?(What is he....?)

I think it occurs in any conText where 'is' is used without the pronouns I, you, he, she etc. or a name of thing or person just after it (in irish).For example:
"That's the man who is married"
"Sin é an fear atá pósta"

BUT
"The man is going there"
"Tá an fear ag dul ansin"

I hope that helps