While almost all the reactions in your body take place in, and even include interactions with, water, there are some that require a hydrophobic milieu. Moreover, you need something to keep the outside out, and the inside in…a membrane…which is made of something called lipids.

As I said earlier, a common theme in biology is how large "macromolecules" from subunits, usually known as monomers.
Proteins are arguably the most important and, inarguably, the most diverse of all the macromolecules.
Each protein begins as a long strand of hundreds (or thousands) of amino acids. Since there are 20 different amino acids commonly used, 100 amino acids would have 20¹⁰⁰ possible sequences.
In practice, you won't see all possible ones and they are not randomly put together. Instead, the information in the DNA is used to specify what sequence is made (through a process we will learn about).
These chains then fold into complex structures you have seen.

A common theme in biology is how large "macromolecules" from subunits, usually known as monomers. Really, I'm underselling this point. You will see it over and over for the next several months.
Two linked together is a "dimer," three is a trimer...you get the idea. We usually get lazy after "tetramer" and start calling them "oligomer" for groups that are in the range of 5-10 and then "polymer," when you get to many units…hundreds or thousands…even more. Hey…one common organic compound we will get to know is known as an "ester." What do you think we call a fiber made of many of these linked together?

In some sense, all science comes down to understanding energy. If someone ever asks you why something happens, you can answer: "The second law of thermodynamics." It's never wrong, but also may not be very helpful unless you can make the connection to more local causes. This is the beginning of the discussion, with a biological theme.

In the same way that one can trace your heritage using your DNA, the evolutionary history of all living things can be fit to a tree of life. You might be surprised where you fall.