These are called essential fatty acids. You can imagine the arrangement by picturing a flagpole with three banners flying in a stiff wind. The pole would be the glycerine and the banners would be the fatty acids. It is the unsaturated fats which, depending on where those spaces are, can be 'essential' to the body. Fats and fatty acids are used for many purposes in the body.
Cholesterol is needed to make hormones.
Fats, in general, help as a storage of energy for when we do not get enough to eat and as a padding to keep internal organs from bouncing around. Fats are also needed as protection around the nerves and to help keep cell membranes fluid so cells can change shape as needed, for instance, when red blood cells need to squeeze through capillaries. Fats that are saturated are used primarily as energy storage. As we eat more saturated fats, blood cholesterol levels tend to increase and body fat increases. Butter, lard, bacon 'grease', margarine and solid shortening are all forms of saturated fats.