Learning basic chess tactics is essential for any improving player. Understanding tactics can help you take advantage of your opponents' mistakes, and help you avoid making mistakes of your own. In most cases, games are won and lost because of tactical errors; for beginners, this can mean something as simple as not seeing a certain piece can be captured.
In fact, the most basic tactic of all is just that - the capture of an undefended piece. In chess terms, we say pieces which are attacked but not defended are en prise.
In the diagram above, Black has an undefended knight on b7. White can simply play Rxb7, winning the knight.