本人(běn rén) - oneself, in person; the person concerned; I (formal) in Mandarin

本人 (běn rén) has two lives. In official language it means the person concerned, and it is the word that stops somebody else collecting your parcel or signing your form: 请本人办理 means come and do it yourself.

Standing alone as a subject it becomes a formal I, the register of a declaration or a signed statement: 本人同意 is the Chinese equivalent of the undersigned agrees. After another pronoun or a name it is emphatic instead, so 他本人 means he himself and 我本人 marks a personal view as distinct from an official one.

The trap is swapping it in for 自己. 我本人做的 is a stiff, official-sounding claim; 我自己做的 is what you say about the meal you cooked. Use 本人 when a form, a rule or a formal disclaimer is involved, and 自己 the rest of the time.