To fizz is to froth or bubble over. If you shake up a soda, it will fizz out of the bottle when you open it.
When something fizzes, you hear a hissing sound as the tiny gas bubbles are released. Any carbonated beverage will fizz when it's opened or poured, the way seltzer fizzes in a glass, or beer fizzes and foams in a mug. The word fizz, which has been in use since the 1600s, is imitative — in other words, it sounds just like what it means.