Sea level rises… sure but?

How the hell does it fall? I literally had to look up on Google "how does sea level rise and fall lower reduce decrease go down" because all it thinks i want is OMG THE SEA LEVEL IS RISING GLOBAL WARMING!!!!!!!! PANIC!!!! No, how is this not an asked question? The sea rises and falls periodically throughout the year due to seasons, but what causes it? And say we didn't have global warming, how would it decrease over the years? Is it because of still water, ice, and how it floats above the surface? It can't be that simple can it?