A "main piece" is another word for "dress". It's the core of your coordinate (aka "coord") that you build everything else off of. Here are some of my favorite dresses from my wardrobe. As you can see, AP is my favorite brand as I like their prints and their dresses fit me without alteration. Dresses come and go, so I will primarily be posting things I don't intend to sell any time soon.

Angelic Pretty
                   

Baby the Stars Shine Bright

Other Brands
 

Metamorphose