"He is a good man."
Translation:Fear maith is ea é.
The verbs tá and is have different uses in Irish, and there is a lot more about them coming your way. Worth getting a good grammar book, but broadly tá goes with adjectives to describe things and is with nouns and pronouns to identify, categorise and classify people and things.
"I am cold" is describing a transient feature or experience. "It is cold" is describing a transient feature of the weather. Both use tá. Tá mé fuar, ta sé fuar.
"I am a man" = a permanent feature, an identifying characteristic. "I am a cold man" = a permanent characteristic, I am taciturn, unemotional, unresponsive - in a word, cold. Both use is. Is fear mé Is fear fuar mé Duine fuarchúiseach is ea é (He is a cold, unresponsive person).