The chief function of your gallbladder is getting gallstones. Gallstones are stone-like concretions of bile that sit happily in your gallbladder doing nothing particular, until something prompts them to move.
Vigorous exercise, eating fat food and changes in room temperature will make your gallbladder contract, and get those little stones moving.
The fun bit is when the stones try to exit the gallbladder through the very thin and convoluted little duct that leads to the liver (and the bowels). Said duct does not like knobby stone-like objects being forced through itself, and it manifests its unhappines with a violent pain, known as a "biliary colic".
If the stone gets stuck in there, then you are in serious shit: the bile backs up, and part of it passes into your blood. You turn yellow, like in hepatitis. And it is time for a nice quick trip to the hospital, for a duct toilette, and gall bladder remotion - a common surgical procedure.

I got rid of my gallbladder some months ago, and I sure do not miss it. It was making my life miserable. No avocados. No eggs. No quesadillas.

One fun thing about gallbladder pain is that it gets "radiated", that's to say, it can surface quite far away from the little green fiend.