Always remember that the quantity exchanged is the lesser of what producers and consumers wish to exchange at a given price. Note that with a tax, the price that consumers pay will differ from the price that producers receive. Note also that the quantity produced will equal the quantity consumed. Note that with a subsidy, the price that consumers pay will differ from the price that producers receive. Note also that the quantity produced will equal the quantity consumed.
Price floors involve a minimum price that can be charged.
To be effective, they must be set above the market equilibrium price. Note, that with an effective price floor, the price paid by consumers equals the price received by producers. However, the quantity produced will differ from the quantity consumed. Price ceilings involve a maximum price that can be charged. To be effective, they must be set below the market equilibrium price.