帮忙 (bāng máng) is a separable verb meaning 'to help, to do a favor' — you can insert words like 个 or 我的 between 帮 and 忙 (e.g., 帮个忙). Unlike 帮 (bāng, HSK2), which directly takes an object (帮我), 帮忙 cannot take an object directly. 帮助 (bāngzhù, HSK3) is more formal and used in writing; 帮忙 is everyday spoken Chinese.