Predicative adjectives are adjectives used in their base forms, i.e. without an ending. This is the form in which they occur in a dictionary (also known as citation form). In the sentence they come later than the noun they qualify:
De universiteit van Sheffield is groot.
The University of Hull is large.
Alan is aardig.
Alan is nice.
Alans kamer is gezellig.
Alan’s room is nice/cosy.
Sara vindt het boek mooi.
Sara thinks the book is beautiful.
Here is an example in context (from a weather forecast):
De eerste oktoberdag was ongekend zonnig en zacht. Dinsdag wordt het weer minder fraai.
The first day in October was uncommnly sunny and mild. On Tuesday the weather will be less pleasant.
Zonnig, zacht and fraai occur in their citation form. Zonnig en zacht follows oktoberdag, and (minder) fraai follows weer.