There are small parts between Genes in an Operon that does not encode for any amino acids. What is the purpose of these parts?
The regions between the genes on a prokaryote operon are transcribed into the messenger RNA  but are not translated into proteins.  Because they are not translated, they are characterized by the general term UnTranslated Regions (UTRs).  A typical operon having two genes is shown in this diagram from Wikipedia: 



The UTR which occurs between the protein-coding genes contains the sequence for a ribosomal binding site (RBS) in the transcribed mRNA.  An RBS is a site where a ribosome can attach to the mRNA so that the Start codon of the following gene is in the correct position to begin translation of the protein.  (Of course, the 5' UTR preceding the first gene also has an RBS sequence.)  An RBS contains a particular nucleotide sequence to match up with a complementary sequence of the ribosomal RNA of the ribosome; this sequence is known as the Shine-Dalgarno sequence.

(Note that these inter-gene UTRs are not called introns; introns occur only in eukaryotes and occur within a gene, between the Start and Stop codons.)