Think of it like a map that provides a snapshot of all the planetary coordinates at the exact time of your birth. Every individual’s birth chart (also know as a natal chart) is completely unique. The location, date, and time of your birth is all that is needed to calculate your birth chart.
Visually a chart is a 360 degree wheel divided into 12 sections. Each section is named after the famous constellations or zodiac signs that we are all familiar with (i.e Aries, Leo, Gemini, …). Your planets are plotted onto the wheel to see which sign they fall into to. For example, to calculate your Sun sign we look at which zodiac constellation the Sun was sitting in at the time of your birth.