What should my fermentation look like?
To the left you see a normal, healthy fermentation in "high krausen". It's got a nice thick krausen going, and there's lots of activity in the airlock. To the right, you see an equally healthy fermentation. These two images look different for a number of reasons; they may be at different stages of the process, one yeast might be more active than the other. All of this is normal. Your krausen could be darker or lighter depending on your beer. Your krausen will fall back into the beer more or less depending on the strain you're using, and then you'll know you're well on your way to tasty, delicious homebrew.
These images are examples of infection. With proper sanitizing and healthy yeast, you will minimize the risk of infection. Every fermentation is different, of course, but by and large, fluffy foamy scummy thing is good! Yay beer!