Correct identification of duck species is a critical skill for the beginning duck hunter.
While many types of ducks may be taken during duck season, the limit for different species varies and is subject to change year to year.
For instance, in 2015 the daily limit in California is seven ducks. Of those seven, only two pintail are allowed, only three scaup, and only one canvasback. Yes, ONE canvasback. It is highly recommended to NOT waltz into the Colusa Check Station with two canvasbacks -- it's illegal. For more info on limits so you don't shoot the illegal stuff, see the CA Department of Fish and Game Waterfowl Regulations.
Short of hanging out with me, picture practice is probably the best way to work on your identification skills. Ducks can be divided into two general categories -- dabbling ducks (aka puddlers) and divers -- based on their feeding habits, anatomy, habitat, etc. That's how I've broken it down for you. Check out the links below to learn about the most commonly seen ducks and geese in California.
Dabblers
Divers
Geese
Don't shoot me!
After you feel comfortable with the targets, make sure you also recognize the species to avoid and then test yourself.