Recent content by Little girl being erased

I don't quite understand critical angle, is the angle of incidence the crictical angle?, how do you know which one is the critical angle in a diagram, I don't understand it. Please explain in a very basic, less wordy way. Any help would be appreciated, I have a test on wednesday..please help.

...please help i have a test? theres a problem I'm struggling with : A frog, hiding behind a rock on the river bed can see a faint reflection of the fish in the surface of the water. as the fish swim further the refletion becomes brighter and brighter. Explain why. I don't understand it, please...