For full tutorials, search "gumpaste flowers" at www.youtube.com. There are some really nice videos up with step by step instructions.
Flowers like the roses and calla lilies I used for Jordan's cake start with a gumpaste center that is dried overnight and then petals added around it. For roses, I like to complete one layer a day and let the previous layer dry, if I have the time.
Like buttercream drop flowers, gumpaste drop flowers are simple cutouts with dragee centers, great for fillers or to add a touch of whimsy to cupcakes.
A few pics of the process: