In simple words
Karka is the Vedic name for the sign Cancer. It is ruled by Moon and is movable (a starter).
If your Moon was in Karka, read "As your Moon sign". If Karka was rising when you were born, read "As your lagna". Your chart page in Vedic mode shows both.
As your Moon sign
With the Moon in Karka, your emotions are deep, tender and closely tied to family and home. You care for others instinctively and remember everything that touched your heart. Feeling safe is the foundation of your wellbeing.
As your lagna (rising sign)
With Karka rising, you come across as caring, receptive and protective. Home and mother figures often play a large part in your story. Learning to ask for care keeps your own reserves full.
Growing with Karka
Make your home a place that restores you, then let some of that care flow back to yourself.
Vedic signs are measured from the stars (the sidereal zodiac), about 24° behind the Western ones. That is why many people's Vedic sign is one sign earlier than their Western sign.