sorry my computer can not type mandrain at this moment, i hope you can understand english.
Acctually first name in our mandrain way is surename, but for westen way, their sure name is at the back, and their given name (the name given by their father or mother) is at the front part, so called First Name. 究竟First name 係姓? 定係名? is depend on where you filling the form it, but normally, if they use english, use should follow the westen style, so you must fill in you given name at the first name field.