Constructive waves are low energy waves with a stronger swash than backwash. Where there are less than 8 waves breking each minute they tend to be constructive waves.
Constructive waves tend to deposit material and build up a beach.
By contrast, destructive waves have much higher energy. They are much larger in height. They have a weak swash but a strong backwash, and they therefore erode the beach by pulling sand and shingle (beach materials) down the beach as water returns to the sea.
The Wycombe High School website has some excellent animations of both constructive and destructive waves. You can see them here. Alternatively, you could look at the Curriculum Bits website animations.