The 4th house represents how it all began -- your roots and childhood. Also, your mother and/or any maternal influences you may have, plus your current home, family and domestic life. It is, after all, ruled by sensitive and nurturing Cancer!
Any emotional repercussions from your childhood are rooted in the 4th house, as is family life and family background in general, domesticity and real estate.
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.