Everyone enjoys the convenience of swiping a credit or debit cards to make purchases, but that is also how many scammers get a hold of your card numbers. Many credit card thieves dont even steal your actual credit card, instead they use something called a skimmer that steals the credit card numbers. A skimmer is a device that reads the magnetic strip on the card and they usually onto another card so scammers then have a credit card to make purchases.
The most likely place for skimmers is an outdoor ATM or a pay at the pump gas station. This allows the scammers access to the device to install the skimmer. Other places that could be considered high risk would be at a restaurant where the server has access to your card or online shopping with a site that you are not familiar with.
Be sure to check your card statements often to be sure and catch any fraudulent charges. Report these charges to your card company immediately.