Hi,
For example, if you set the "Cart retain period" option to 1 week, the carts will be kept in the database for one week before being removed. That means that if a user comes, add some products to his cart, leave your website, and come again 3 days after that, he will still have his cart.
(please note that I'm talking about logged in users. For logged out users, you need to take into account the session lifetime option of the joomla configuration too).
The option "Frequency of the check for the cart" is the frequency at which this is checked. We set it at once per day by default.
The plugin never unconfirms an order. It only changes the status from created to cancel.
Once the order has been paid and thus confirmed, the status won't be changed.
You need to publish that plugin and make sure that the options are what you want. Then, if the cron is setup properly it will work automatically.