Protein sequencing is a technique to determine the amino acid sequence of proteins. It involves hydrolyzing proteins into amino acids, separating the amino acids, and using techniques like chromatography to identify the order of the amino acids. There are chemical methods like Edman degradation and physical methods like mass spectrometry to sequentially determine the order of amino acids from the N-terminal to C-terminal end of the protein. Understanding amino acid sequences provides insight into protein structure and function.