Hello my client wants his categories and subcategories to show on the front page.

How do I accomplish this

www.banner.on.ca

Examples can be seen on this site, the topic North Middlesex hs the subcategories Ailsa Craig - Nairn - Parkhill in it. But they don't show. And if I just put those categories in themselves then only one category shows at one time.

I would like all categories to show in module without tabbed navigation.

Choose the subcategories in each K2 content module. It will fetch items from all selected and you can use the Show category option to show in which subcategory each item belongs to.