What are Hydrocarbons?
Because both carbon and hydrogen were common in nebulae, hydrocarbon molecules are very common in space. Many of these molecules are small, like methane, but others are very big, involving hundreds of atoms. One of the interesting things about carbon is that can easily make itself into long chains of carbon atoms, so it is easy to build big molecules using carbon as a building block.
Out in space, the biggest hydrocarbon molecules are amino acids. But here on Earth, those amino acids were able to hook up with each other to make protein molecules. One protein molecule can contain hundreds of amino acids in various combinations. All living cells are made out of those protein molecules, so all living cells are made out of hydrocarbons: your body, fish, sweet potatoes, trees, cheese, seaweed. Anything that was once alive is also made of hydrocarbons, so that also includes things like oil (made out of plants that died billions of years ago), gasoline and plastic (made out of oil), rubber, wood, food, alcohol, and many medicines like antibiotics.