Chloride, as opposed to chlorine, is an ion so it can be made by simply putting NaCl (sodium chloride) into water since it is an ionic compound. That means that if you mix salt in a cup of water the salt will dissolve.
I'm not sure if you meant chlorine, but that is made industrially by electrolysis of NaCl. Can make NaCl by mixing HCl + NaOH which gives water and NaCl (table salt).
If you meant just Cl, well that is a radical. Chlorine is diatomic, and that is made by taking chlorine gas and exposing it to light or heat. It will create a chlorine radical, but these are very reactive and do not just sit around.