An indirect tax is charged on spending on a good or service. It raises the producer's cost, so the amount supplied is lower at every possible market price. This shifts the supply curve upwards. Without the tax, the original equilibrium is at the intersection of supply $S$ and demand $D$, with price $P_0$ and quantity $Q_0$. With the tax, the new equilibrium is at the intersection of the shifted supply curve $S+tax$ and demand $D$, with buyer price $P_b$ and lower quantity $Q_1$. At quantity $Q_1$, the original supply curve gives the seller price $P_s$.