This layout is centered and typically a horizontal layout. The blooms are central in the frame surrounded by your greenery. 

This layout is meant to mimic the look of a bouquet with the blooms at the top and center and more stems towards the bottom. 

The free floating layout is where every bloom and piece of greenery is seen equally with space around it to create a visual collage. This is a great choice if your bouquet is very "bloom heavy" with many different types of flowers.