Loops are the connections between categories and interests.
To begin your loop, selecting your category on the post page. This is the commercial (sales) thing that people are buying. Penniloop places categories first so that users can easily determine how much your item is worth to them. Once you select the category you have the option of a sub-category.
Sub-categories aren't required but they help your buyers find exactly what they need (like coats in winter and flip-flops in summer).
After the category is added, move on to the interest. If you're not sure where your item fits, use the dropdown to browse the options. If you're still not seeing an exact match, try adding the interest first and the category afterwards.
We suggest making a post "template" to begin with; something basic that you can edit and test with. From there, you can see which topics your items fit in best with.