system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: The different types of fats, trans fats, saturated/unsaturated, etc, and which ones are "good" or "bad"
gpt
The other answers in this thread are right from an organic chemistry perspective, but you are asking about it from a medical/health perspective. Saturated and trans fats are bad, and unsaturated ones are good.

Imagine you eat a burger. it goes in your mouth, then to your stomach, then your pancreas releases a bunch of enzymes that break it down further and it gets absorbed in your small intestine. It crosses the border of your small intestine into your blood. Then the carbohydrate, fat, and protein filled blood goes to your liver. Then the liver does different things with it, but ultimately it converts all the excess protein, carbohydrates, and various types of fat into the standard type of fat that your body uses for storage. Then it sends it out to different parts of your body for storage (like your butt and thighs). 

But now say that the liver wants to withdraw fat from the bank and use it for energy. It needs a molecule to go to the fat cells in your butt and withdraw the fat and bring it back. This molecule is called a high density lipoprotein (HDL or good cholesterol) and it is made out of unsaturated fat. 

The worst thing about fat is not that it makes you look unhealthy. It's that it clogs up your arteries, which means your heart has to work harder to move blood around, which can result in heart failure. The chunks of fat can also break off and cause heart attacks and strokes. The best thing about HDL and the unsaturated fats they are made of is that HDL goes around and scrapes off the fat stuck in your arteries. 

So monounsaturated fats, polyunsaturated fats, and omega fatty acids are considered good because they help make the molecule that removes fat from your body. The other kind of fats help deposit more fat in your body.