One of the strangest things in Irish is that there is no single word for yes and no. (Although the forms tá and níl are sometimes used). Answering questions requires that you use the affirmative or negative with the correct form of the verb used in the question.

Questions are normally formed by adding the construct 'an' before the verb. The 'an' is not usually pronounced, instead relying on the tone of voice to imply a question, but the word does cause an urú in most words beginning with a consonant (not l, m, n, r, s).

An ólann tú tae? — Do you drink tea?

The answer to this question, as shown above, would be either:

Ólaim — yes, I do, or
Ní ólaim — no, I don't

It is immediately obvious that you've got to pay quite a bit of attention when someone asks a question, since you need to know what, exactly, they are asking you in order to figure out the right answers. However, in most cases, it appears that tá and níl would probably be appropriate if you don't know the right forms.

.If the question is posed as,

Ba mhaith liom cupa tae? —Would you like a cup of tea?

Then the answer would be

Ba mhaith — yes, I would, or
Níor mhaith — no, I wouldn't