Why do manager get more salary than labourer?

There are a couple of reasons for this, but basically it boils down to that they have greater responsibilities, so they're compensated more highly.

A manager may be a former laborer who can advise and mentor the laborers working under him if they have difficulties or run into a situation they don't know how to handle. This expertise is obviously worth something.

Even if they're not (this sometimes happens in tech companies, where the technically skilled employees may be managed by someone with a business degree who knows very little about the actual technology involved), the manager is expected to know in general terms how much work a particular project might involve (or at least, which of his employees he could ask that question of to get a reliable estimate) and then estimate the costs for that project and divide the workload over several employees to deliver the project within the desired timeframe. Again, this kind of knowledge is worth something.

Finally, managers are expected to keep the employees under them happy and productive (happiness is secondary, as far as most companies are concerned, but employees who are actively unhappy tend not to be productive and that's a bad thing) and to minimize conflict between them (which again reduces productivity: if Alex hates Bob and goes out of his way to sabotage Bob's work, or at least be as unhelpful as he can get away with being, then Bob's not going to be as productive as he could be and Alex is wasting some of his own time as well). A good manager will minimize conflict and reduce that "as unhelpful as he can get away with" to "not really all that unhelpful", and again, that's worth something.