Mesha, the ram, and why it is not your sun sign
Mesha is Aries in the sidereal zodiac. In this tradition the rising sign, the lagna, leads the chart. The Sun's sign is one fact among nine.
Mesha is the ram, the first thirty degrees after the Lahiri starting point. Western sun-sign columns also say Aries and mean a different sky, because they start from the tropical equinox. If a website told you that you are an Aries and a pandit told you that your lagna is Vrishabha, you may both be looking at real numbers. You are not looking at the same number.
In the Parashari habit used here, the lagna is the house of the body and the hour. Mesha lagna is a chart that rose in the ram at the minute you were born, at that latitude. It is not a personality you can collect from a birthday alone. Without the clock, the lagna is a guess, and the app will not guess it for you.
Mars rules Mesha in the standard scheme. Rulership is a technical relation used for dignity and for reading a house. It is not a licence to say that Mesha people start fights. Some do. The reason is not printed on the sign.