What makes a fatty acid unsaturated or saturated? What do they look like?

There's usually 14-20 carbons joined by single covalent bonds, with hydrogen attached to every single carbon. there's a methyl group on one end and a carboxyl group on the other end. they're saturated when theyre joined by a DOUBLE covalent bond, and you can have your trans saturated version with hydrogen atoms on opposite sides of the covalent carbon bond, or the cis version, where the hydrogen atoms are on the same side