You can setup more than one alert for the same category by entering search words or filters separated by a comma. For example, if you want to receive craigslist alerts on a car & a bike on sale, enter: car, bike against the Filter field.
You can view your alerts by going to Manage My Alerts link on the top right menu. If you are logged in, this will display all the alerts you have setup. If not, it will prompt you to enter your email address to which a direct link to your alerts will be emailed.
You can delete your alerts by going to Manage My Alerts link on the top right. This will display your alert criteria sorted by category. You can click on the delete button for a specific alert to delete it.