The Slider has a couple of options which can be found in slider-options.php. These options only apply if you are using the built-in capability to display selected images from your site's Media Library.
The Slider can display a random image from a selection highlighted in the Media Library (typically on the front page of your site, but it can be called on any page). However there will be occasions where it would be good to be able to fix the first image shown on the page, for example to highlight an AGM or an event. This image can be specified by its ID (this is revealed by hovering over a link in the Media Library and looking to see the 'post' number in the URL).
The displayed image is changed to another from the selection every ten seconds by default, but the interval can be specified in milliseconds.