What is the difference between prokaryotic genes, eukaryotic genes and operon?

Genes are genes - although unique, the construction is similar. However, the complexity of the expression and regulation is different between prokaryotes and eukaryotes.

the operon is the entire repertoire of structures needed to express a gene in either prokaryotes or eukaryotes. Some can be repressors - slow/stop expression or drive expression. In many ways it is easier to study gene expression in prokaryotes (no nuclear envelope and DNA construction) when compared to the nuclear envelope-enclosed eukaryote genome.

In your text, they will invariably explain how the operons control the production of (+/-) protein expression ( lac operon is the historical one) to respond to environmental changes.