include following js
//= require jquery.remotipart
//= require jquery.ui.widget
//= require jquery.iframe-transport
//= require jquery.fileupload
//= require jquery.fileupload-ui
//= require jquery.fileupload-fp

in js write the following

$('.user_window').fileupload({
dataType: 'json',
url: url
})

here user_window is a class of html element where you want to drop the file from a dir or somewhere else

url is the path where you want to send your request

you can find deep detail here

https://github.com/blueimp/jQuery-File-Upload