A rowing machine is a piece of exercise equipment that allows you to simulate rowing a boat. Not a row boat, but a scull, such as the Oxford varsity 'crew' row in races against Cambridge. The difference between a scull and a row boat is that the seat slides back and forth and the rower uses his or her legs as well as the arms and back to pull back on the oars.
Using a rowing machine gives you a more complete workout than stairsteppers or treadmills, which mainly exercise your lower half. To operate a rowing machine, sit on the seat with your knees bent and take the handle, which simulates the 'oars,' in both hands. Pull back with the arms and back while pushing your seat back by extending your legs.
Muscle groups in your arms, legs and back are all involved in using a rowing machine, which is one of the most complete aerobic workout machines available. You can typically adjust tension in some way to make the pull harder to accomplish and thus get a more vigorous workout.
You can use a rowing machine at your local gym, although you will have to wait your turn -- rowing machines are one of the more popular pieces of equipment for time-pressed exercisers. Or you can purchase a home rowing machine and row whenever you feel like it. Most home models have a way of folding down for under-bed storage, or some similar space-saving feature.
Rowing machines vary considerably in features, stability and feel, with the cheaper models offering a faint echo of the feel you will get from a more expensive model. How smoothly the seat slides on the track will have a considerable effect on how enjoyable the workout is, and consequently on whether or not you will be inclined to pursue the exercise, so buying a cheap rowing machine that has a lurching, swaying seat is a waste of money. Take a test cruise in your sports equipment store before purchasing a rowing machine to avoid a costly equipment mistake.
Of course, you can't find exercise gear without computerized readouts any more, and rowing machines come with counters that will measure a number of variables, from miles 'traveled' to calories burned. Readouts of this kind are mainly useful for motivating yourself and tracking progress. Can you beat your best time? Are you able to row longer and farther, burn more calories? Keeping a log of these stats can keep you rowing through the I-hate-exercise doldrums.