From the Globe and Mail

As the wine flows, it undergoes turbulence, accelerating its contact with air. Oxygen can enhance a wine’s aroma and also, especially in the case of reds, soften astringent tannins. The wine will taste more complex and smoother. Even young bottles can benefit, especially those sealed under screw cap. If you don’t own an aerator… you can accomplish much the same effect with a decanter or any pitcher. Empty the bottle into the vessel, then pour it from the decanter into glasses. Or, if you don’t have a decanter, swirl the wine in your glass.

While you are at it, you may as well learn how to taste wine properly.