The 3rd house represents your immediate environment: how you communicate with others (specifically, your relationship with your siblings) and also how you gather data and information.
The people who shaped you at an early age, like teachers and neighbors, are represented here, as is the town in which you currently live, the streets and businesses and overall community you face every day. And as communication planet Mercury and talkative Gemini rule over the 3rd house, anything that has to do with talking, networking and technology is represented here.
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.