What role do stop codons play in protein synthesis?

The sequence of nucleotides, coded in triplets (codons) along the mRNA, that determines the sequence of amino acids in protein synthesis. The DNA sequence of a gene can be used to predict the mRNA sequence, and the genetic code can in turn be used to predict the amino acid sequence.

The above answer already provides the background so I'm just going to answer your question. The stop codons aid to end the translation of mRNA sequence to proteins or in other words, terminate translation. When the ribosome reads the stop sequence, no nucleotide will bind and the polypeptide chain synthesized will be released.