ならでは is used to express that something is unique to, distinctive of, or only possible because of a particular noun. It carries a strongly positive nuance, emphasizing that the quality, experience, or characteristic in question cannot be found anywhere else or with anyone else.
It attaches directly to a noun and is often followed by the particle の when modifying another noun.
The most common pattern is ならではの placed between two nouns, where the first noun is what makes something special, and the second noun is the unique quality or thing.
ならでは can also appear at the end of a sentence with だ (or です), meaning "it is something only [noun] can offer."
Unlike simply saying だけ ("only"), ならでは carries an inherent sense of appreciation or admiration. It implies that the thing being described is valuable precisely because of its unique origin. You would not typically use ならでは for something negative.
For example,