The first piece of the function, f(x) = -x+1, has a y-intercept of 1 and a slope of -1. This means it will be decreasing by 1 for every increase in x until it hits the y-intercept of 1.
The second piece of the function, f(x) = x+1, has a y-intercept of 1 and a slope of 1. This means it will start at the y-intercept of 1 and increase by 1 for every increase in x.