To export the jquery.ui gadget, click on "Download" button, save the downloaded file, go to Special:Import on the destination wiki and upload it. Then add the following to MediaWiki:Gadgets-definition page:
* jquery.ui[ResourceLoader|type=general|rights=hidden|hidden]|jquery.ui.js|jquery.ui.css
You must have appropriate permissions on the destination wiki (including the right to edit system messages) and import from file uploads must be enabled.