my understanding is that, first, you have to separate between 'tà' and 'is'.
'Tá' sentences have tbe subject first:
tá sé tuirseach
'is' sentences link two nouns together: 'I am a woman' = 'is bean mé'. Both 'mé' and 'bean' are "things".
In 'is' sentences, the 'predicate' comes first, the subject second:
'is bean í' = 'she is a woman'
Here, 'she' is the 'subject' and 'a woman' is the predicate. We are talking about 'she' and saying that 'woman' is a class of things she belongs to.
'the teacher is a woman' = 'is bean í an muinteoir'
Here, we are talking about a specific teacher. You lean close and point out that she is also a woman.
'the woman is a teacher' = 'is muinteoir í an bhean'
Here, we are discussing a certain woman an you point out that she is a teacher.