Firstly you will need to be logged in as an admin user in order to change the moderation settings. Once logged in, click on the Administration link at the top of the page to access the administration settings.
Select either the Moderation or Site Settings link at the top of the page.
In either page, go to the Moderation Settings section, this will tell you the current setting. To change this setting, select the Moderation Settings link.
Use the radio buttons to toggle between pre-moderation and post-moderation. Post-moderation means that ideas and comments will be published immediately and can be retracted my a moderator if found to be inappropriate. Pre-moderation means that new ideas and comments will not appear on the site until explicitly approved by a moderator.
To find out more about how to moderate challenges, ideas and comments refer to this article.