The tips and notes for the Food 2 skill explain it. The definite article an before masculine nouns beginning in a vowel prefixes t- before the vowel, so an t-aran the bread, an t-athair the father, an t-ubhal the apple.
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This is the good bread would be seo an t-aran math.
In Gaelic the determiners seo this and sinthat go after a definite noun, they don’t work like English this and that that go before the noun.
You can think about them as kinda equivalent of English right here and over there, and then an t-aran seo as the bread right here and an t-aran sin as the bread over there if that helps you.