After you've added products to commercial catalog, you need to add this catalog to Bitrix24 Online Store page. Click Add block > Online store > Products.
By default, all products will be added. But we want to have a separate page for each product category. Let's add only Milk chocolate category to this page. To do that, just click Settings > Catalog settings.
Click Select next to Catalog folder field.
Select the needed category and click Save.
Now there is only Milk chocolate category displayed on this page. You can do the same for other pages and categories.