Butterflies can usually be told from moths (in the UK at least) by the clubbed antennae. Of course most moths are nocturnal but there are plenty of exceptions.
Butterflies and moths make up the Lepidoptera (tile-winged), insects which have small overlapping scales on their wings. These scales are clear in some of the moth photos on this site but you have to use a hand-lens to see them with the naked eye.
There are far more species of moths than butterflies in Europe. In the UK there are about 60 species of butterflies compared with nearly 2,500 moths... though many of these are quite rare and many are tiny.