Amino acids have a carboxylic acid (CO2H), an amine (NH2), and a side chain. In the cases of glycine and valine, the side chains are H and isopropyl. Two amino acids can join each other via the formation of an amide bond. An amide group is a carbonyl carbon attached to an amine nitrogen. I have written the chemical equation below for glycine and valine forming an amide bond.
H2N-CH2-CO2H + H2N-CH(iPr)-CO2H --> H2N-CH2-CONH-CH(iPr)-CO2H
Basically, the carboxylic acid (CO2H) of the glycine joins with the amine (NH2) of the valine to make an amide bond (CONH) in the product. The iPr stands for the isopropyl group on the valine.