Many stations are in fact free, this is because they are funded through advertising. Every 20 minutes of television has ten minutes of commercials (advertisements for products or services). There are other premium stations that have monthly fees to watch them. To get these other premium stations that specialize in things such as Science Fiction, History, Science, Movies etc. you would need to subscribe to a service provider such as a cable service (signals are sent via cables installed in your home) or a satellite service (signals are received via an installed satellite dish). Neither service provider has much in the way of competition so their rates are fairly high. You pay a monthly charge for service and an additional fee for each station above the bare minimum provided with basic service. Although there are a number of people that do subscribe to these premium channels and service , many others just stick with the free stations.

If you use an antenna and receive your signal via VHF/UHF radio transmissions, then yes, it is free. TV stations get their money by selling advertisement time to companies that wish to market their products. Many people get television via cable companies, where a cable carrying the TV signals is run to the person's home. This is called cable television. Others use satellite providers like DishNetwork and DirecTV, where the signal is beamed from satellites and received with a satellite dish receiver. People getting their TV from cable or satellite pay a monthly fee to the cable or satellite TV company. There is a much bigger selection of programs using cable or satellite than is typically available for free.