What is an example of active transport?

Active transport refers to a substance moving from areas in which it has low concentration to an area with high concentration, one example i guess is endocytosis, " the taking in of matter by a living cell by invagination of its membrane to form a vacuole"

A common example of active transport, or moving a substance against its gradient, is the maintaining of a balance of sodium and potassium inside and outside a cell. Obviously too much sodium inside the cell would cause cell death. So, the cell must actively regulate how much sodium is allowed in through the membrane.