干活(gàn huó) - to work, to do manual work, to graft in Mandarin

干活 (gàn huó) is working in the physical, hands-on sense: farm work, building, cleaning, shifting things about. It is colloquial and slightly earthy, and it says nothing about having a job. For employment as a status you want 工作 (gōng zuò).

Being a verb-object compound, it splits. Anything that modifies the work goes in the middle: 干了三个小时的活 (gàn le sān ge xiǎo shí de huó), worked for three hours; 干重活 (gàn zhòng huó), do heavy work. This is the same behaviour as 吃饭 (chī fàn) and 睡觉 (shuì jiào), and it catches learners who treat the compound as one indivisible word.

Two traps with the characters. 活 (huó) here is second tone and means work, not the 活 (huó) of 生活 (shēng huó), to live, even though it is the same character. And 干 (gàn) is a merger of two traditional characters: 幹 (gàn, to do), which is the one here, and 乾 (gān, dry). Simplified script writes both as 干, so the tone is what tells them apart.