Vital to the structure of living things is the way carbon atoms tend to bond together to form a "backbone" or "skeleton" to produce hydrocarbon chains (also rings) as here illustrated by a selected number of the fully hydrogen saturated "alkanes".
Boiling point increases with lengthening of the carbon chain. Unless kept under pressure Methane to Butane quickly boils at room temperature to form a gas. The next longest chains are liquid at room temperature and are used as fast drying solvents for example in dry cleaning of clothes. Then comes oils, greases, waxes, and hard solids such as asphalt used to make roads. Hydrocarbon chains may be hundreds of carbon atoms in length even bonding together to become an almost endless.
Chains with more than three Carbon atoms can form many different structural isomers to make rings, cubes, triangles or branch off. These "isomers" have similar (but not exact for example branched design more easily burned) chemical properties as the straight-chain "n" forms shown.
An abundant source of hydrocarbons is crude oil where decomposed organic matter provides carbon and hydrogen under conditions favorable for their formation. The same hydrocarbons are also found in living things. Methane (swamp) gas is a digestion product. Others (shown below) are used in insect attraction or defense and form waxy coatings on some plants or by bees to make beeswax. The "tails" of membrane forming lipids (phospholipids) are hydrocarbon chains which accounts for their being hydrophobic (repelled by water while attracted to grease/oil) on their tail end.
Hydrocarbons are relatively inert (do not change in form over time) but is easily ignited to "burn" in atmospheric oxygen. This replaces the carbon-carbon bonds holding the hydrocarbon together with oxygen-carbon bonds to produce CO carbon monoxide and CO2 carbon dioxide with the now free hydrogen atoms also being mopped up by oxygen to produce H2O water molecules.
The above by Gary S. Gaulin may be copied as needed for educational use.