Context: Not from the investment banking or trading background. Have been an investor / trader with modest gains. How does one solve for risk in the markets? A

Context: Not from the investment banking or trading background. Have been an investor / trader with modest gains. How does one solve for risk in the markets? As in, mathematically. How does one do short term predictions of prices, with a day or two as the prediction range, with a probability > 0.5.