Glutamic acid hydrochloride is a salt that supplies the amino acid glutamic acid. When it dissolves, it splits into glutamic acid and chloride ions. This makes it different from betaine hydrochloride, which actually donates hydrochloric acid. Keep that distinction clear if you see it in a formula.
Your body uses glutamic acid to build proteins and to make glutamate, a key brain chemical. You also get plenty of glutamic acid from everyday food, so a supplement does not add benefits you cannot obtain through diet.
There is no standard dose for this ingredient. You will spot it mostly inside amino acid blends rather than as a standalone product. Take it with food to avoid stomach upset.