The 1st house represents the way you present yourself, both physically and intellectually. It's the very first impression you make upon the world!
Think of the 1st house as your own representative, speaking for yourself and the childhood experiences that made you who you are in this very moment. Your more aggressive and action-oriented traits are associated with this house, as it ties to fiery Aries and action-planet Mars.
Your birth chart is divided into 12 "houses" which govern specific areas of your life. At the time of your birth, each planet was located in a particular astrological sign and in one of the 12 houses.