Sveika Rusne! There is a difference. For example, 'a work of art' is a fixed phrase. 'The arts' refers to the whole field of artistic endeavors-- theatre, sculpture, painting, dance, etc. 'Art' refers to any one of these in the general aesthetic.

Art = general sense. This is uncountable. The Arts = forms of art. Specifically, all the various artistic endeavours.

's'