A player's table image is the perception other players have of them and their playing style. This perception may or may not be correct, but it affects how other players see the player in question, and how they react to the player's actions.
A key part of basic poker strategy is to always be aware of your table image, and take opportunities to affect your image in a manner you desire. Your table image affects how other players react to you and your actions. You can direct your table image by choosing which hands you expose at the showdown. If you want to have a tight image, you expose a few powerful hands, even if they are not at the showdown (e.g. expose pocket aces or kings, or suited Ace-King). For a loose image, expose weak winning hands like unsuited low connectors.
If you have a tight table image, that means your opponents believe you only play premium starting hands. If you know you have such an image, you can make use of that fact and occasionally bluff at the pot if it appears no one else has a very strong hand.
If you have a loose table image, that means opponents believe you will be betting and playing with any two cards, and will tend to call your bets and raises, believing you probably have nothing. This can result in very large pots when you have a strong hand.
Always be aware of your table image by keeping track of the hands you have exposed. Consider: what do other players think you might be playing? Then use that information to anticipate their moves and react to them accordingly.