With the pronunciation zuō, this is a colloquial verb meaning 'to cause trouble' or 'to be fussy/high-maintenance', used in casual speech (e.g. 别作了 'stop acting up'). It contrasts with the more common reading zuò (to do, to write, to compose). Note that 作 also appears as a bound-form noun pronounced zuō in words like 作坊 (workshop) and 作料 (seasoning), but those are noun uses, not covered under the verb POS of this entry.