If you take a look at this website you'll see the different feet for some makes
I assume you mean what are the different feet used for?
General purpose foot will have room for the needle to swing through wide stitches, but enough foot to hold the fabric and move it through against the feed dogs. This is the one you use most.
A straight stitch foot will have a little hole so that the needle only goes through a small area and the fabric can't move to give a neat plain straight stitch.
Plastic wide toe foot is good when you need to see what you are sewing onto such as applique (sewing a piece of fabric onto another with a wide satin stitch).
Teflon coated foot is good for slippery fabrics, it grips well.
A roller foot is great for textiles like leather and vinyl which don't feed nicely.
Then there are lots of feet for turning the fabric to sew it such as a rolled hem (these come in different widths so you can turn 2mm, 4mm or 6mm for example).
Felled foot (like the side seam on your jeans) joining two fabrics in a felled seam
Then there are feet for quilting and darning where you need to move the fabric smoothly in different directions, these will be small foot area and open stitching space usually.
Walking foot is a special one, part of the foot moves because a part of it clips around the needle bar and the up and down movement then activates the foot so its little teeth help to move the fabric from the top to supplement the normal feed dogs below. Pfaff machines actually built this function into their machines some years ago to give even feed from top and bottom. Great for quilting thick fabric sandwich or sewing together fabrics that want to slip or not feed smoothly.
There is also similar info here http://sewmamasew.com/blog2/2009/06/feet-feet-feet/
which may help you to see the different uses and feet available.
Most manufacturers will sell their machine with 4 or 5 of the most used feet but often have more to buy aftermarket. And many feet between companies look very alike so if you have a clip on foot from one brand it may work on another machine with a clip on foot.
I hope that this is what you were asking.