What exactly is hydrocloride and it's purpose? ¿?

In chemistry, hydrochlorides are salts resulting, or regarded as resulting, from the reaction of hydrochloric acid with an organic base (mostly amines). An archaic alternative name for "hydrochloride" is muriate, derived from hydrochloric acid's ancient name: muriatic acid.
Converting insoluble amines into hydrochlorides is a common way to make them water-soluble. This is particularly desirable for substances used in medications.

source wikipedia.org

It has no purpose, its just the chemical salt of some drugs. Think of it as the drugs last name.