Add the slideshow widget to where you want to display it on the homepage, by going to "Customize > Widgets" choosing the "slider" widget.
Once you've added the slider to the widgets area, a selection of options will appear.
To choose the category you want to display, select a category from the drop-down "Category" options.
These are the categories you have created for the articles on your site.
If you want to learn how to create a unique category to combine stories from multiple categories into one slider, click here.
Make sure to hit the "Save & Publish" button at the top of the screen to set your changes live.