In very basic terms a peptide is like a tiny protein. Know that a peptide is classified as a compound of a chain of 2 or more amino acids. However, peptides are distringuished from proteins on the basis of size. As a basic rule, a peptide contains 50 or fewer amino acids linked by peptide bonds. A peptide bond is formed by dehydration synthesis. Dehydration synthesis is a chemical reaction in which water is removed from the compound. Peptides are referred to by the number of amino acids present. For instance, you should know the following groupings: dipeptides are those that have two amino acids. Tripeptides are those with three amino acids. Oligopeptides contain, for instance, less than 10-15 amino acids. And any peptide that has more than 10-15 amino acids are called polypeptides. For further clarification, here's the wikipedia link on peptides.
Again, peptides are short chain amino acid linked by a peptide bond.
The body uses these amino acids to grow muscle by secreting growth hormone (GH) that is already stored in the body. The body never slows production of (GH) it only becomes harder to activate with age. Activating (GH) can aid in recovery and fat loss. That's why consuming carbohydrate and protein supplementation can be highly beneficial in boosting body metabolism. Peptides produce growth hormone. The best known peptide hormones are (hGH) and insuline-like growth factor 1 (or 1GF1). Both are anabolic. That means they promote cell growth and proliferation.
For supplementation, concentrate mostly on amino acid (BCAA), protein, and carbohydrate consumption. Otherwise, you'll start treading in murky waters that can get treacherous.