Items upload . new

Hello
Today I install omeka s.
My question is about media.
When I add a file, image etc with upload, I have an error

Omeka S encountered an error

Why ?

these is my error

Omeka\File\Exception\InvalidThumbnailerException
ImageMagick error: cannot determine path to ImageMagick command.

is ok now.
The problem was that I need ImageMagick
Sorry for the questions
gus