Sculptors mold various materials into 3-dimensional objects meant to be viewed from multiple different angles.
Some sculptors focus on site-specific installations, creating works that are intrinsically connected to the places where they are exhibited. Such works would be difficult to relocate to other sites, for artistic reasons but sometimes also for very practical reasons.
Technically, paintings are also 3-dimensional objects, but the visual interest is mostly 2-dimensional and the backs of paintings are generally hidden by the walls on which they are placed. Sculptures, on the other hand, are usually exhibited so that they can be viewed from almost any angle whatsoever, including from above, and in some cases even from below.
Of course some sculptors are also painters, but generally few painters are also sculptors.