It is important to have the correct set of strings fitted to your guitar, especially if you are a beginner. Until you build enough strength in your hands to bend strings, light gauge or low tension strings are recommended.
A reputable music store which sells guitar strings should be able to assist with this. In time, you may wish to experiment with heavier string guages, as they produce a stronger tone. It is important to change your strings regularly, as old strings go out of tune easily and are more difficult to keep in tune.