well the application does not really work like that.
You can set global permissions in the admin for edit usergroups on as to what permissions the groups can do.
You can refine permissions under edit categories for every category what group can view what content upload to what cats and post comments to ads sure.
I have never seen anyone who has every asked for such an option to be honest. You essentially want a usergroup that can upload but not view any content. Not exactly sure you can try setting permissions under edit categories for the group you wish can not view but can upload but I think your end result would be kind of different.