You might think you know what work is, like homework, or having to pick up your room, right? But to scientists, work has a more definite meaning: work is force x distance.
That means that you can measure work by measuring how much force, or energy, it took to move something, and multiplying that by how far you moved it (or how many of them you moved). It takes a certain amount of energy to push a plow through the fields, and it takes more energy to push it up and down four furrows than it takes to push it down only one furrow. It takes a certain amount of energy to pick up one bowling ball, and it takes twice as much energy to pick up two bowling balls. If you move two bowling balls one mile, you've done the same amount of work as moving one bowling ball two miles.
Bibliography and further reading about work: