Hi @Mlwhiddon, welcome to the Community.
Item modifiers allow you to add small adjustments on the item when you add it to a sale - for example, say you offer a cheese pizza, your modifiers would be toppings.
Categories help organize the types of items you have - example here would be categorizing your items "Food" and "Drinks."
Hope that helps! Read more about Item Modifiers and Creating Categories in our Support Center.
