The function F(x) = 2x + 3 is a linear function that increases at a rate of 2 units for every 1 unit increase in x, with a y-intercept of 3. The function f(x) = x^2 + 2x - 3 is a quadratic function that is symmetric around the y-axis, with its vertex at the point (-1,0) and intersecting the x-axis at x = -3 and x = 0.