Describe the different types of isomers.

The two main types of are structural isomers and stereoisomers.
Structural Isomers have the same molecular formula but a different arrangement of atoms. The position of the functional group can change resulting in two molecules that have different structures but the same molecular formula. For example the -Cl group on a butane can be located on the 1st or the 2nd carbon in a chain. Or the functional group it self can be different. For example C₃H₆O can have an aldehyde or a ketone as a functional group.
Stereoisomers have the same molecular formula, but a different spatial arrangement. These are divided into conformational isomers which can be interconverted by rotating around (sigma) bonds and configurational isomers which can be interconverted only by breaking and reforming bonds.
Furthermore, configurational isomers are divided into cis/trans isomers and occur in alkenes and cycloalkanes. And optically active isomerism due to the spatial arrangement of 4 different group on a chiral carbon.