Uploading a file is easy if you see the upload link. I didn’t.
To ensure you see it you have to change the setting in LocalSettings.php
$wgEnableUploads = true;
You may get an error **Could not create directory “mwstore://local-backend/local-public/ **and some more alpha characters. This turned out a simple permission problem. You have to set the permission of your images directory to 777