Workers’ control means exactly what it says: the working class and its representatives in the factories have the right to inspect the books of a company or industry etc., to check and control all ingoings and outgoings, and the actions of management.
In The Transitional Programme, Trotsky explains that the first step towards actual control of industry is the abolition of “business secrets”. Business secrets, the accounts and the books, are of course used to justify all manner of attacks on the working class such as wages reductions, lay-offs, sackings and increases in working hours.
When the bosses claim bankruptcy, or claim they are losing profits, and demand such things, workers’ control allows the workers to inspect the books and ascertain the real situation. The idea is to lift the veil, to show the working class the detailed workings of the capitalist system as a step towards its elimination.
The immediate tasks of workers’ control should be to explain the debits and credits of society: looking first at individual enterprises to determine the share of the national income of individual capitalists and of course the ruling class as a whole. Another task of workers’ control should be to reveal to society the squandering of human labour and the naked pursuit of profits, as well as to expose secret deals, swindles, and corruption inherent in the system.