State is the highest level of organization for Humans out there. One of the cornerstones of Statehood is ability to hold a monopoly on force on a given territory (also known as Sovereignity). That fact alone allows the State to levy taxes and rake in money in many other ways. Real estate tax, Capital gains tax, Inheritance tax & others all come to mind. All of this ends up in the budget of the State. This is controlled by government (in its different forms, ranging from Dictatorship to Liberal Democracy), which spends it, according to its preferences.

Therefore, you make business with the State both as an individiaul Citizen as well as an Entrepreneur/Business owner. Whenever you buy something in a retail store, you pay VAT (Value Added Tax), which basically means that State takes away a part of "earnings" from the retailer, which you actually pay for as a buyer.

However, making business with the State is not a one-way relation. Many times, State does offer opportunities for private business to earn something. Opportunities come in different forms, however. 

(PPP's) Public - Private Partnerships:  This is a way for a State (or any local governmental instance) to see the projects for public benefit get done without full public funding, but be partially funded by the private businesses and banks. 

Various subsidies: By giving out subsidies, State hopes to spur developement in areas, for which it seems, that they would be benefitial on the long run for the economy and the State nonetheless. Especially, business activities that have some sort of strategic value, often get subsidized. One could also get subsidy in the form of low interest loans from commercial banks, subsidy provided by the State. 

Grants. Grants are an outright "gift" of the State to different organizations, be it either NGO's that fill a certain role in society at lerge or businesses as well. Of course they have a system in place to prevent misuse (although often it is hard to prevent it) of funds. 

Supra-national (also known as "International") organizations, like United Nations, variuos regional and continential organizations, like Europe Union, African Union and more, also often provide funding in different forms, for which you can apply, if you meet the selection criteria they put forward. This can make a world of difference for some business or organization. Many do survive mostly on such funding, which is often too rigid for a fast moving world of today. 

There is an well established chart of business relations revolving around Customer and Business. "C" stands for Customer, while "B" stands for Business. So, according to that you can have C2C, B2B, C2B, B2C relations. However, now that we started to mention State as a strong player in economy as well, we could just as well add "G" for Government (Governance).

Lets take an example in the form of a governmental contractor. Normally, they would fall somewhere in the category of B2B (Business, making business with other business). In the sense, we can remove the second "B" and replace it with the "G", as the buyer of the governmental contractor would be Government itself (one of its branches, that is military). Another example would be na Individual citizen, lets says that he recently lost his job. Hence, he would be entitled to have some sort of unemployment benefit in order to keep him up on his feet, while he is looking for another employment. In this case, he would be a "C" - Customer, doing business with the State AKA "G" - Government. Government would have required him to activelly search for a new job and to provide occasional paperwork on his social status (to check for eligibility for unemployment benefits). Many States do have various conditions in place for unemployment benefits, as this is often a hot topic during election campaigns.