Compounds built around carbon are called organic compounds. Some are natural, such as sugars, proteins and the hydrocarbons in crude oil. Others are synthetic, which means people make them, such as plastics and many medicines. There are millions of different organic compounds.
This huge number is possible because carbon atoms form four strong covalent bonds and can bond to other carbon atoms. They join into long chains, branched chains and closed rings, and the chains can be any length. Hydrogen, oxygen and other atoms can then bond to the carbon atoms.
Organic compounds fall into families of similar compounds. Alkanes such as methane, ethane and propane are one family. They contain only carbon and hydrogen joined by single bonds, and each member differs from the next by the length of its carbon chain. Members of one family react in a similar way, so the family gives a pattern that makes the compounds easier to predict.