Both Form-5 & 6 require sending to the ESI authority with CA certification on Form-5. Form-5 is the summary of paid challans for six months, and Form-6 details the employee contributions during the six months (e.g., total working days, total wage, and total contribution paid against the employee).
Further information is provided in both forms and is easily available to download from CiteHR.
Regards, Sandeep.