Here is the link for Bernina Gathering foot how-to. These instructions are good for other brnads as well.
http://weallsew.com/2011/10/05/the-f...athering-feet/

Re the notches on the ruffler--that is how you select the density of the gathers. Experiment to choose how much 'ruffle you want. The newer gathering feet for later machines are sooo different. Mine is an Elna and the ruffle is decided by the stitch length & tension...but you can still sew to project at same time it's making ruffle. The older type can be adjusted to make nice pleats, also.