Drag it where you want it on the page. You can add new images to it, just like any other image widget - simply select or upload.
Please try and make these images a sensible size - if you upload images that are very high resolution, then it will impact the performance - on your template, I'd resize images to be no more than 1024px wide and under 100kb. It will work with larger images, but as I say, may impact performance if you use lots of images in your slideshow.
The settings for the slideshow:
Changing from default in the top right allows some styling options around where the navigation controls are displayed (if you choose to display them).
Animate settings control the slideshow - pause speed is the time on each slide in milliseconds. Animation speed is the time spent moving from one slide to the next.
The dimensions control allow you to set the width and height of the slideshow. By default it is full width - you can enter an exact size or resize manually.
Resize manually to control the slideshow when you have a mixture of portrait and landscape images.