For items in a list tool, managing publication is done via the Publish Tab. Sitemason allows you to control three different publication dates for the Post Time, Archive Date, and Expiration Date. Additionally, you can set the publication status and access to the post.
The Post Time is the time and date the article will appear on your website. By default, it's set to the time you create the item. If you set a Post Date to a future date and time, the post will not be live on your site until that time in the future. This is especially helpful for press releases and promotions where you know a very specific time that something has to be live, but might not necessarily be at a computer when it does.
By default, all items are listed in perpetuity in chronological order. If you'd prefer to keep your main list of items, like your portfolio gallery, current, and only keep relevant items in the main view, you can optionally Archive items. These items are still live on the website, but instead of being listed with your current content, they're available when searching archives.
Ask your web developer about using Archives if it sounds like something you might want to use on your site.
When an item is expired, it is taken off the website. It will no longer be accessible anywhere on the site, and its contents are removed from search. An example use of expiration dates might be having a distinct window of opportunity for a promotion. Like "be on our website before Friday to get details on this promotion".
An additional control for items is to set the Publication Status to "Approved" or "Pending". These controls are used mainly for workflow purposes. For example, if a supervisor wants to see all copy before it's published, a junior editor might write a post and set it to "Pending", and the supervisor would then review the work, and if fit to publish, set to article to "Approved".