Your rising sign or ascendant is the zodiac sign that was rising on the eastern horizon the moment you were born. It is the lens through which you see the world.
The rising sign is specific to the time and place of your individual birth and is considered, in Astrology, to be as important and significant as the Sun and Moon signs because all other aspects of the birth chart are filtered through this sign.
The rising sign is the path we take to our Sun sign.
The Sun is why we are here, the rising /ascendant sign is how we get there.