Punching holes in the yard will improve its health while conditioning the soil. Aeration is just that, allowing a path for air--particularly oxygen--to penetrate the root bed and stimulate soil activity. In addition, nutrients and moisture are made readily available where they are needed to grow a thick stand of grass.
For small areas of lawn, a hand spike aerator provides a more-than-adequate solution for opening pores into the soil. Built with a T-handle and a step for pressing the spikes into the ground by foot, manual spike aerators make quick work of aeration. Spike aerators also are available as lawn tractor attachments.
Plug aerators aggressively remove thatch and compacted soil. Whereas a spike aerator punches holes into the soil the size of the spike, plug aerators remove small round cylinders of soil and drop them on top of the ground. Exposing additional fresh ground in this manner allows for more of the substances lawns need to thrive. Plug aerators are available as a pull-behind mower attachment for riding lawnmowers.
Not a spike aerator, and more gentle on the lawn than a plug aerator, a bladed aerator is often used during mowing. The blades, shaped like wheels, run along a single shaft and are pulled behind the mower. This light form of aeration cuts slits into the soil, allowing the soil to breath and accept water and nutrients readily.