The fiction y=x+3 is a linear function, which means that its graph is a straight line. The slope of the line is 1, which means that for every increase of 1 in the x-value, the y-value increases by 1. The y-intercept of the line is 3, which means that the line passes through the point (0, 3). As you move along the line from left to right, the y-value increases at a constant rate.