Taxes and job opportunities are the two main contributions of private sectors when it comes on economic growth. Not all countries, especially those in the third world, has the financial capability to give more job opportunities to their people and this one is being aided by private companies or sector.Another is in form of taxes wherein for them to operate they need to comply with registrations on the local government and that includes fees. Well, it is a mutual relationship also. Private companies get the opportunity to generate profit from their businesses on their target countries. Everything's studied therefore they know that they will be making more than how much they would be putting into it.
One of the major role of private sector in economic growth is public-private partnership (PPP). The government wants to have a public service that needs to be provided to the public, however, they do not have sufficient resources to provide the said service (i.e., roads, bridges, railways, airports). Hence, they engage the private sector to build the infrastructures in return of some profit.
Indeed one of the best examples. In the country where I live, railways are one of their biggest contribution. It is being used on a daily basis which makes it simply profitable and same goes with government sector who are earning a percentage from its profit.