帮 (bāng) is the most common, everyday verb for 'to help' – you use it directly before the person you help (帮我) or the action (帮做饭). 帮忙 (bāng máng) is a set phrase meaning 'to do a favor' and cannot take a direct object; 帮助 (bāng zhù) is more formal and often used in writing.