It can be used as an adjective or an adverb, depending on the context.
Here are some examples:
* Car newydd (New car)
* Dillad newydd (New clothes)
* Mae'r ty yn newydd (The house is new)
* Mae hi'n gwisgo gwisg newydd (She is wearing a new dress)
* Mae'r newydd yn rhyfeddol (The news is amazing)